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/adapters/project.test.ts

@@ -0,0 +1,27 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+const invoke = vi.fn();
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: (...args: unknown[]) => invoke(...args),
+}));
+
+import { TauriProjectGateway } from "./project";
+
+describe("TauriProjectGateway invoke payloads", () => {
+  beforeEach(() => invoke.mockReset().mockResolvedValue({}));
+
+  it("reads and updates the project context under .ideai", async () => {
+    invoke.mockResolvedValueOnce("# shared");
+    await expect(new TauriProjectGateway().readProjectContext("proj-1")).resolves.toBe(
+      "# shared",
+    );
+    expect(invoke).toHaveBeenCalledWith("read_project_context", {
+      projectId: "proj-1",
+    });
+
+    await new TauriProjectGateway().updateProjectContext("proj-1", "# next");
+    expect(invoke).toHaveBeenCalledWith("update_project_context", {
+      request: { projectId: "proj-1", content: "# next" },
+    });
+  });
+});