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>

frontend/src/features/layout/LayoutGrid.test.tsx

@@ -8,7 +8,7 @@
  * rather than xterm's visual output. They stay robust whether or not xterm
  * bailed.
  */
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import { render, screen, waitFor, fireEvent } from "@testing-library/react";
 
 import type { Gateways } from "@/ports";
@@ -90,8 +90,10 @@ describe("LayoutGrid (with MockLayoutGateway)", () => {
     });
   });
 
-  it("closing a cell removes THAT cell and keeps its sibling (closes the right terminal)", async () => {
+  it("closing a cell removes THAT cell and keeps its sibling without killing its session", async () => {
     const layout = new MockLayoutGateway();
+    const terminal = new MockTerminalGateway();
+    const closeSpy = vi.spyOn(terminal, "closeTerminal");
     const initial = await layout.loadLayout("p1");
     const a = leaves(initial)[0].id;
     // Split A → container c with children [A (index 0), b (index 1)].
@@ -102,8 +104,18 @@ describe("LayoutGrid (with MockLayoutGateway)", () => {
       newLeaf: "b",
       container: "c",
     });
+    await layout.mutateLayout("p1", {
+      type: "setSession",
+      target: "b",
+      session: "running-session-b",
+    });
 
-    renderGrid(layout);
+    const gateways = { layout, terminal } as unknown as Gateways;
+    render(
+      <DIProvider gateways={gateways}>
+        <LayoutGrid projectId="p1" cwd="/home/me/proj" />
+      </DIProvider>,
+    );
     await waitFor(() =>
       expect(screen.getAllByTestId("layout-leaf")).toHaveLength(2),
     );
@@ -117,6 +129,7 @@ describe("LayoutGrid (with MockLayoutGateway)", () => {
     expect(
       screen.getByTestId("layout-leaf").getAttribute("data-node-id"),
     ).toBe(a);
+    expect(closeSpy).not.toHaveBeenCalled();
   });
 
   it("closing the other cell keeps the opposite sibling", async () => {