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/project/context.rs

@@ -0,0 +1,115 @@
+//! Project-level context stored under `.ideai/CONTEXT.md`.
+//!
+//! This context is model-agnostic and shared by every agent/profile launch. It is
+//! deliberately project-local: deleting `.ideai/` removes the context together
+//! with every other IdeA artefact for that project.
+
+use std::sync::Arc;
+
+use domain::ports::{FileSystem, FsError, RemotePath};
+use domain::Project;
+
+use crate::error::AppError;
+
+use super::meta::{join_root, IDEAI_DIR};
+
+/// Project-context file name inside `.ideai/`.
+pub const PROJECT_CONTEXT_FILE: &str = "CONTEXT.md";
+
+/// Input for [`ReadProjectContext::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ReadProjectContextInput {
+    /// Project whose `.ideai/CONTEXT.md` should be read.
+    pub project: Project,
+}
+
+/// Output of [`ReadProjectContext::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ReadProjectContextOutput {
+    /// Markdown content. Empty when the file does not exist yet.
+    pub content: String,
+}
+
+/// Reads `.ideai/CONTEXT.md` tolerantly.
+pub struct ReadProjectContext {
+    fs: Arc<dyn FileSystem>,
+}
+
+impl ReadProjectContext {
+    /// Builds the use case.
+    #[must_use]
+    pub fn new(fs: Arc<dyn FileSystem>) -> Self {
+        Self { fs }
+    }
+
+    /// Executes the read.
+    ///
+    /// # Errors
+    /// Returns [`AppError::FileSystem`] on non-missing filesystem failures, and
+    /// [`AppError::Store`] if the file is not valid UTF-8.
+    pub async fn execute(
+        &self,
+        input: ReadProjectContextInput,
+    ) -> Result<ReadProjectContextOutput, AppError> {
+        match self.fs.read(&project_context_path(&input.project)).await {
+            Ok(bytes) => {
+                let content = String::from_utf8(bytes)
+                    .map_err(|e| AppError::Store(format!("project context is not UTF-8: {e}")))?;
+                Ok(ReadProjectContextOutput { content })
+            }
+            Err(FsError::NotFound(_)) => Ok(ReadProjectContextOutput {
+                content: String::new(),
+            }),
+            Err(e) => Err(AppError::FileSystem(e.to_string())),
+        }
+    }
+}
+
+/// Input for [`UpdateProjectContext::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct UpdateProjectContextInput {
+    /// Project whose `.ideai/CONTEXT.md` should be overwritten.
+    pub project: Project,
+    /// New Markdown content.
+    pub content: String,
+}
+
+/// Overwrites `.ideai/CONTEXT.md`.
+pub struct UpdateProjectContext {
+    fs: Arc<dyn FileSystem>,
+}
+
+impl UpdateProjectContext {
+    /// Builds the use case.
+    #[must_use]
+    pub fn new(fs: Arc<dyn FileSystem>) -> Self {
+        Self { fs }
+    }
+
+    /// Executes the update.
+    ///
+    /// # Errors
+    /// Returns [`AppError::FileSystem`] if `.ideai/` cannot be created or the
+    /// context file cannot be written.
+    pub async fn execute(&self, input: UpdateProjectContextInput) -> Result<(), AppError> {
+        self.fs
+            .create_dir_all(&RemotePath::new(join_root(&input.project.root, IDEAI_DIR)))
+            .await?;
+        self.fs
+            .write(
+                &project_context_path(&input.project),
+                input.content.as_bytes(),
+            )
+            .await?;
+        Ok(())
+    }
+}
+
+/// Absolute path to `<root>/.ideai/CONTEXT.md`.
+#[must_use]
+pub fn project_context_path(project: &Project) -> RemotePath {
+    RemotePath::new(join_root(
+        &project.root,
+        &format!("{IDEAI_DIR}/{PROJECT_CONTEXT_FILE}"),
+    ))
+}

crates/application/src/project/mod.rs

@@ -14,11 +14,18 @@
 //! - [`ListProjects`] — list known projects from the registry.
 
 mod close;
+mod context;
 mod create;
 pub(crate) mod meta;
 mod open;
 
 pub use close::{CloseProject, CloseProjectInput, CloseProjectOutput, CloseTab, CloseTabInput};
+pub use context::{
+    project_context_path, ReadProjectContext, ReadProjectContextInput, ReadProjectContextOutput,
+    UpdateProjectContext, UpdateProjectContextInput, PROJECT_CONTEXT_FILE,
+};
 pub use create::{CreateProject, CreateProjectInput, CreateProjectOutput};
 pub use meta::ProjectMeta;
-pub use open::{ListProjects, ListProjectsOutput, OpenProject, OpenProjectInput, OpenProjectOutput};
+pub use open::{
+    ListProjects, ListProjectsOutput, OpenProject, OpenProjectInput, OpenProjectOutput,
+};

crates/application/src/project/open.rs

@@ -7,9 +7,7 @@ use domain::{AgentManifest, Project, ProjectId};
 
 use crate::error::AppError;
 
-use super::meta::{
-    from_json_bytes, join_root, ProjectMeta, AGENTS_FILE, IDEAI_DIR, PROJECT_FILE,
-};
+use super::meta::{from_json_bytes, join_root, ProjectMeta, AGENTS_FILE, IDEAI_DIR, PROJECT_FILE};
 
 /// Input for [`OpenProject::execute`].
 #[derive(Debug, Clone, PartialEq, Eq)]