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/infrastructure/tests/pty_adapter.rs

@@ -35,10 +35,7 @@ fn size() -> PtySize {
 
 /// Drains an output stream to a single `Vec<u8>` on a worker thread, returning
 /// the collected bytes or panicking if it does not finish within `TIMEOUT`.
-fn drain_with_timeout(
-    stream: domain::ports::OutputStream,
-    timeout: Duration,
-) -> Vec<u8> {
+fn drain_with_timeout(stream: domain::ports::OutputStream, timeout: Duration) -> Vec<u8> {
     let (tx, rx) = mpsc::channel();
     let worker = thread::spawn(move || {
         let mut all = Vec::new();
@@ -80,10 +77,7 @@ async fn write_is_echoed_back_through_output_stream() {
     // `cat` echoes its stdin back to stdout; we feed it a line then close stdin
     // by killing it, and assert we saw the echoed bytes.
     let pty = PortablePtyAdapter::new();
-    let handle = pty
-        .spawn(sh_spec("cat"), size())
-        .await
-        .expect("spawn cat");
+    let handle = pty.spawn(sh_spec("cat"), size()).await.expect("spawn cat");
 
     let stream = pty.subscribe_output(&handle).expect("subscribe once");
 
@@ -118,10 +112,7 @@ async fn subscribe_output_is_re_subscribable_for_reattach() {
     // first view detaches (drops its stream), a second view re-attaches and
     // still receives subsequent output — the core of the no-kill navigation fix.
     let pty = PortablePtyAdapter::new();
-    let handle = pty
-        .spawn(sh_spec("cat"), size())
-        .await
-        .expect("spawn cat");
+    let handle = pty.spawn(sh_spec("cat"), size()).await.expect("spawn cat");
 
     // First attachment: subscribe, observe an echo, then drop the stream
     // (simulating a view tearing down on navigation — NOT a kill).