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/domain/src/events.rs

@@ -106,6 +106,25 @@ pub enum DomainEvent {
         /// The project whose index was rebuilt.
         project_id: ProjectId,
     },
+    /// A project's memory grew past the recall budget while no embedder is
+    /// configured (strategy `none`): the first moment a semantic embedder would
+    /// help (ARCHITECTURE §14.5.5, LOT C3). Published **at most once per session per
+    /// project** (and never again once the user chose "ne plus demander"); the
+    /// frontend surfaces a one-time, dismissible suggestion. Carries the detected
+    /// local environment and the compiled-in capabilities so the UI never proposes
+    /// a strategy this binary cannot run.
+    EmbedderSuggested {
+        /// The project whose memory crossed the budget.
+        project_id: ProjectId,
+        /// Whether an Ollama-style local embedding server was detected (best-effort).
+        ollama_detected: bool,
+        /// Ids of the recommended ONNX models already present in the local cache.
+        onnx_cached: Vec<String>,
+        /// Whether the HTTP capability (`localServer`/`api`) is compiled in.
+        vector_http_enabled: bool,
+        /// Whether the in-process ONNX capability (`localOnnx`) is compiled in.
+        vector_onnx_enabled: bool,
+    },
     /// Raw PTY output (usually routed to a dedicated channel, not this bus).
     PtyOutput {
         /// The session.