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/tests/project_usecases.rs

@@ -22,7 +22,8 @@ use domain::{Project, ProjectId, ProjectPath, RemoteRef};
 
 use application::{
     CloseProject, CloseProjectInput, CloseTab, CloseTabInput, CreateProject, CreateProjectInput,
-    ListProjects, OpenProject, OpenProjectInput,
+    ListProjects, OpenProject, OpenProjectInput, ReadProjectContext, ReadProjectContextInput,
+    UpdateProjectContext, UpdateProjectContextInput,
 };
 
 // ---------------------------------------------------------------------------
@@ -75,11 +76,7 @@ impl FileSystem for FakeFs {
     }
 
     async fn create_dir_all(&self, path: &RemotePath) -> Result<(), FsError> {
-        self.0
-            .lock()
-            .unwrap()
-            .dirs
-            .insert(path.as_str().to_owned());
+        self.0.lock().unwrap().dirs.insert(path.as_str().to_owned());
         Ok(())
     }
 
@@ -221,6 +218,8 @@ struct Env {
     bus: SpyBus,
     create: CreateProject,
     open: OpenProject,
+    read_context: ReadProjectContext,
+    update_context: UpdateProjectContext,
 }
 
 fn env() -> Env {
@@ -238,6 +237,8 @@ fn env() -> Env {
         Arc::new(bus.clone()),
     );
     let open = OpenProject::new(Arc::new(store.clone()), Arc::new(fs.clone()));
+    let read_context = ReadProjectContext::new(Arc::new(fs.clone()));
+    let update_context = UpdateProjectContext::new(Arc::new(fs.clone()));
 
     Env {
         store,
@@ -245,6 +246,8 @@ fn env() -> Env {
         bus,
         create,
         open,
+        read_context,
+        update_context,
     }
 }
 
@@ -301,6 +304,44 @@ async fn create_registers_project_in_store() {
     assert_eq!(stored[0].name, "Demo");
 }
 
+#[tokio::test]
+async fn project_context_lives_under_ideai_and_missing_reads_empty() {
+    let env = env();
+    let out = env.create.execute(input("Demo", "/p")).await.unwrap();
+
+    let missing = env
+        .read_context
+        .execute(ReadProjectContextInput {
+            project: out.project.clone(),
+        })
+        .await
+        .unwrap();
+    assert_eq!(missing.content, "");
+
+    env.update_context
+        .execute(UpdateProjectContextInput {
+            project: out.project.clone(),
+            content: "# Shared\n\nUse pnpm.".to_owned(),
+        })
+        .await
+        .unwrap();
+
+    let bytes = env
+        .fs
+        .read_file("/p/.ideai/CONTEXT.md")
+        .expect("project context written under .ideai");
+    assert_eq!(String::from_utf8(bytes).unwrap(), "# Shared\n\nUse pnpm.");
+
+    let read_back = env
+        .read_context
+        .execute(ReadProjectContextInput {
+            project: out.project,
+        })
+        .await
+        .unwrap();
+    assert_eq!(read_back.content, "# Shared\n\nUse pnpm.");
+}
+
 #[tokio::test]
 async fn create_publishes_project_created_event() {
     let env = env();
@@ -543,7 +584,10 @@ async fn close_without_workspace_skips_persistence() {
         .await
         .unwrap();
 
-    assert!(store.saved_workspace().is_none(), "no persistence when None");
+    assert!(
+        store.saved_workspace().is_none(),
+        "no persistence when None"
+    );
 }
 
 #[tokio::test]