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/ports/index.ts

@@ -13,6 +13,8 @@ import type {
   AgentDrift,
   AgentProfile,
   DomainEvent,
+  EmbedderEngines,
+  EmbedderProfile,
   FirstRunState,
   GitBranches,
   GitCommit,
@@ -78,6 +80,20 @@ export interface AgentGateway {
    * launched a second time — one live session per agent).
    */
   listLiveAgents(projectId: string): Promise<LiveAgent[]>;
+  /**
+   * Rebinds an already-live agent session to another visible layout cell without
+   * respawning the CLI process. Used when a background agent is opened in a cell,
+   * or when a live session is moved from a now-detached/closed cell.
+   *
+   * Backends that do not yet support agent-session rebinding may omit this
+   * method; the UI will show the session as running elsewhere but cannot attach
+   * it from a different cell.
+   */
+  attachLiveAgent?(
+    projectId: string,
+    agentId: string,
+    nodeId: string,
+  ): Promise<LiveAgent>;
   /** Creates a new agent from scratch; returns the created agent. */
   createAgent(projectId: string, input: CreateAgentInput): Promise<Agent>;
   /** Reads an agent's `.md` context by agent id. */
@@ -156,6 +172,11 @@ export interface LiveAgent {
   agentId: string;
   /** The node (layout leaf) hosting the agent's live session. */
   nodeId: string;
+  /**
+   * The live PTY session id, when the backend exposes it. Required for opening
+   * a background/running agent in a new visible cell without respawning it.
+   */
+  sessionId?: string;
 }
 
 /**
@@ -253,6 +274,10 @@ export interface ProjectGateway {
   openProject(projectId: string): Promise<Project>;
   /** Closes a project by id. */
   closeProject(projectId: string): Promise<void>;
+  /** Reads the shared project context stored at `.ideai/CONTEXT.md`. */
+  readProjectContext(projectId: string): Promise<string>;
+  /** Overwrites the shared project context stored at `.ideai/CONTEXT.md`. */
+  updateProjectContext(projectId: string, content: string): Promise<void>;
 }
 
 /** Layout: load the terminal grid tree and apply mutating operations (L4). */
@@ -458,6 +483,29 @@ export interface ProfileGateway {
   configureProfiles(profiles: AgentProfile[]): Promise<AgentProfile[]>;
 }
 
+/** Input for {@link EmbedderGateway.saveEmbedderProfile}. */
+export interface SaveEmbedderProfileInput {
+  profile: EmbedderProfile;
+}
+
+/**
+ * Embedder configuration (L14 / lot C2). Drives the memory/embedder settings
+ * panel: lists the configured embedder profiles, the available engines (with
+ * build-time feature flags so unavailable strategies can be shown disabled),
+ * and persists / removes profiles. Changing the active embedder takes effect at
+ * the next app start. Mirrors the four backend embedder commands.
+ */
+export interface EmbedderGateway {
+  /** Lists the configured embedder profiles (transparent: no secrets). */
+  listEmbedderProfiles(): Promise<EmbedderProfile[]>;
+  /** Creates or replaces (by id) a single profile; returns the saved profile. */
+  saveEmbedderProfile(profile: EmbedderProfile): Promise<EmbedderProfile>;
+  /** Deletes an embedder profile by id. */
+  deleteEmbedderProfile(embedderId: string): Promise<void>;
+  /** Describes the available engines + build feature flags + detection. */
+  describeEmbedderEngines(): Promise<EmbedderEngines>;
+}
+
 /**
  * The full set of gateways the app depends on, injected via the DI provider.
  * The composition (real vs mock) is chosen in `app/`.
@@ -474,4 +522,5 @@ export interface Gateways {
   template: TemplateGateway;
   skill: SkillGateway;
   memory: MemoryGateway;
+  embedder: EmbedderGateway;
 }