feat(memory): config embedders (LOT C2) + suggestion contextuelle (LOT C3) + contexte projet partagé

- LOT C2 (§14.5.3) : use cases de configuration des embedders déclaratifs
  (List/Save/Delete + DescribeEmbedderEngines : modèles ONNX recommandés,
  environnement local détecté, stratégies compilées). UI EmbedderSettings.
- LOT C3 (§14.5.5) : suggestion contextuelle best-effort à l'activation quand la
  mémoire dépasse le budget de recall sans embedder configuré (event
  EmbedderSuggested, anti-spam 1×/session, « ne plus demander »).
- Contexte projet partagé .ideai/CONTEXT.md (model-agnostic) injecté à tous les
  agents/profils au lancement, avant la persona. UI ProjectContextPanel.

Tests : backend workspace vert (0 échec) ; frontend 306/306.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/application/src/embedder/usecases.rs

@@ -0,0 +1,245 @@
+//! Embedder configuration use cases (LOT C2). Each is a single-responsibility
+//! struct carrying its ports as `Arc<dyn Port>` and exposing one `execute`.
+//!
+//! - [`ListEmbedderProfiles`] / [`SaveEmbedderProfile`] / [`DeleteEmbedderProfile`]
+//!   — CRUD over the persisted [`EmbedderProfile`]s through the
+//!   [`EmbedderProfileStore`] port.
+//! - [`DescribeEmbedderEngines`] — a read-only view of the engines available to the
+//!   "configure an embedder?" UI: the recommended ONNX model catalogue, a best-effort
+//!   snapshot of the local environment ([`EmbedderEnvInspector`]), and which strategies
+//!   are actually compiled into this binary.
+//!
+//! Hexagonal boundary: the application depends on the domain ports and on plain
+//! data only. The static engine catalogue and the compiled-capability flags are
+//! **injected** at the composition root (the infrastructure owns `reqwest`/`fastembed`,
+//! never the application).
+
+use std::sync::Arc;
+
+use domain::ports::{EmbedderEnvInspector, EmbedderProfileStore};
+use domain::profile::{EmbedderProfile, EmbedderStrategy};
+
+use crate::error::AppError;
+
+// ---------------------------------------------------------------------------
+// ListEmbedderProfiles
+// ---------------------------------------------------------------------------
+
+/// Output of [`ListEmbedderProfiles::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ListEmbedderProfilesOutput {
+    /// All configured embedder profiles (empty when none configured ⇒ `none`).
+    pub profiles: Vec<EmbedderProfile>,
+}
+
+/// Lists the configured embedder profiles from the store.
+pub struct ListEmbedderProfiles {
+    store: Arc<dyn EmbedderProfileStore>,
+}
+
+impl ListEmbedderProfiles {
+    /// Builds the use case from the [`EmbedderProfileStore`] port.
+    #[must_use]
+    pub fn new(store: Arc<dyn EmbedderProfileStore>) -> Self {
+        Self { store }
+    }
+
+    /// Lists configured embedder profiles.
+    ///
+    /// # Errors
+    /// [`AppError::Store`] on persistence failure.
+    pub async fn execute(&self) -> Result<ListEmbedderProfilesOutput, AppError> {
+        Ok(ListEmbedderProfilesOutput {
+            profiles: self.store.list().await?,
+        })
+    }
+}
+
+// ---------------------------------------------------------------------------
+// SaveEmbedderProfile
+// ---------------------------------------------------------------------------
+
+/// Input for [`SaveEmbedderProfile::execute`]: the raw fields of the profile to
+/// upsert (validated into an [`EmbedderProfile`] entity).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SaveEmbedderProfileInput {
+    /// Stable identifier (e.g. `"local-onnx-minilm"`). Non-empty.
+    pub id: String,
+    /// Display name. Non-empty.
+    pub name: String,
+    /// Embedding strategy driving which concrete adapter is used.
+    pub strategy: EmbedderStrategy,
+    /// Model identifier, when the strategy needs one.
+    pub model: Option<String>,
+    /// Endpoint URL for a server/API strategy.
+    pub endpoint: Option<String>,
+    /// Name of the env var carrying the API key (never the key itself).
+    pub api_key_env: Option<String>,
+    /// Length of the vectors this engine produces. Non-zero.
+    pub dimension: usize,
+}
+
+/// Output of [`SaveEmbedderProfile::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SaveEmbedderProfileOutput {
+    /// The saved (validated) profile, echoed back.
+    pub profile: EmbedderProfile,
+}
+
+/// Persists (creates or replaces by id) a single embedder profile, after building
+/// and validating the entity.
+pub struct SaveEmbedderProfile {
+    store: Arc<dyn EmbedderProfileStore>,
+}
+
+impl SaveEmbedderProfile {
+    /// Builds the use case from the [`EmbedderProfileStore`] port.
+    #[must_use]
+    pub fn new(store: Arc<dyn EmbedderProfileStore>) -> Self {
+        Self { store }
+    }
+
+    /// Validates then saves the profile.
+    ///
+    /// # Errors
+    /// - [`AppError::Invalid`] if the profile's invariants are violated (empty
+    ///   `id`/`name`, zero `dimension`),
+    /// - [`AppError::Store`] on persistence failure.
+    pub async fn execute(
+        &self,
+        input: SaveEmbedderProfileInput,
+    ) -> Result<SaveEmbedderProfileOutput, AppError> {
+        let profile = EmbedderProfile::new(
+            input.id,
+            input.name,
+            input.strategy,
+            input.model,
+            input.endpoint,
+            input.api_key_env,
+            input.dimension,
+        )
+        .map_err(|e| AppError::Invalid(e.to_string()))?;
+        self.store.save(&profile).await?;
+        Ok(SaveEmbedderProfileOutput { profile })
+    }
+}
+
+// ---------------------------------------------------------------------------
+// DeleteEmbedderProfile
+// ---------------------------------------------------------------------------
+
+/// Input for [`DeleteEmbedderProfile::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DeleteEmbedderProfileInput {
+    /// Id of the embedder profile to delete.
+    pub id: String,
+}
+
+/// Deletes an embedder profile by id.
+pub struct DeleteEmbedderProfile {
+    store: Arc<dyn EmbedderProfileStore>,
+}
+
+impl DeleteEmbedderProfile {
+    /// Builds the use case from the [`EmbedderProfileStore`] port.
+    #[must_use]
+    pub fn new(store: Arc<dyn EmbedderProfileStore>) -> Self {
+        Self { store }
+    }
+
+    /// Deletes the profile.
+    ///
+    /// # Errors
+    /// [`AppError::NotFound`] if the id is unknown, [`AppError::Store`] on
+    /// persistence failure.
+    pub async fn execute(&self, input: DeleteEmbedderProfileInput) -> Result<(), AppError> {
+        self.store.delete(&input.id).await?;
+        Ok(())
+    }
+}
+
+// ---------------------------------------------------------------------------
+// DescribeEmbedderEngines
+// ---------------------------------------------------------------------------
+
+/// A recommendable local ONNX model, as a plain application value (mirrors the
+/// infrastructure `OnnxModelInfo` data, injected at the composition root so the
+/// application never depends on the infrastructure crate).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct OnnxModelView {
+    /// Stable model id accepted by a `localOnnx` profile's `model` field.
+    pub id: String,
+    /// Human-readable name for the UI.
+    pub display_name: String,
+    /// Length of the vectors this model produces.
+    pub dimension: usize,
+    /// Approximate download/disk size in megabytes.
+    pub approx_size_mb: u32,
+    /// Whether this is the recommended default model.
+    pub recommended: bool,
+}
+
+/// A read-only description of the embedding engines available to the
+/// "configure an embedder?" UI (C2/C3).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct EmbedderEnginesView {
+    /// The curated catalogue of recommendable local ONNX models.
+    pub recommended_onnx: Vec<OnnxModelView>,
+    /// Whether an Ollama-style local embedding server was detected (best-effort).
+    pub ollama_detected: bool,
+    /// Ids of the recommended ONNX models already present in the local cache.
+    pub onnx_cached_models: Vec<String>,
+    /// Whether the HTTP capability (`localServer`/`api`) is compiled into this binary.
+    pub vector_http_enabled: bool,
+    /// Whether the in-process ONNX capability (`localOnnx`) is compiled into this binary.
+    pub vector_onnx_enabled: bool,
+}
+
+/// Describes the engines available to the embedder-configuration UI: the static
+/// ONNX catalogue + compiled-capability flags (injected at construction), enriched
+/// with a best-effort live snapshot of the local environment via the
+/// [`EmbedderEnvInspector`] port. Read-only — emits no event, never fails on the
+/// environment probe (the port is best-effort by contract).
+pub struct DescribeEmbedderEngines {
+    inspector: Arc<dyn EmbedderEnvInspector>,
+    recommended_onnx: Vec<OnnxModelView>,
+    vector_http_enabled: bool,
+    vector_onnx_enabled: bool,
+}
+
+impl DescribeEmbedderEngines {
+    /// Builds the use case from the [`EmbedderEnvInspector`] port plus the static
+    /// engine catalogue and compiled-capability flags (data owned by infrastructure
+    /// and injected at the composition root, so the application stays infra-free).
+    #[must_use]
+    pub fn new(
+        inspector: Arc<dyn EmbedderEnvInspector>,
+        recommended_onnx: Vec<OnnxModelView>,
+        vector_http_enabled: bool,
+        vector_onnx_enabled: bool,
+    ) -> Self {
+        Self {
+            inspector,
+            recommended_onnx,
+            vector_http_enabled,
+            vector_onnx_enabled,
+        }
+    }
+
+    /// Returns the engines view. Infallible in practice: the environment probe is
+    /// best-effort and degrades to "nothing detected".
+    ///
+    /// # Errors
+    /// Never; the `Result` keeps the call site uniform with the other use cases.
+    #[allow(clippy::unused_async)]
+    pub async fn execute(&self) -> Result<EmbedderEnginesView, AppError> {
+        let report = self.inspector.inspect().await;
+        Ok(EmbedderEnginesView {
+            recommended_onnx: self.recommended_onnx.clone(),
+            ollama_detected: report.ollama_detected,
+            onnx_cached_models: report.onnx_cached_models,
+            vector_http_enabled: self.vector_http_enabled,
+            vector_onnx_enabled: self.vector_onnx_enabled,
+        })
+    }
+}