feat(FN-3229): add async planning draft sync to avoid blocking while typing

Merged two changes: a new feature (FN-3229) that syncs planning drafts to the server in real-time while the user types, adding a PlanningModeModal component, a new ai-session-store for managing session state, and a dashboard API route to persist drafts; plus a performance fix replacing a blocking `e

Fusion-Task-Id: FN-3229

packages/dashboard/app/api/legacy.ts

@@ -7235,6 +7235,17 @@ export function pingSession(sessionId: string, projectId?: string): Promise<{ ok
   });
 }
 
+export function updatePlanningSessionDraft(
+  sessionId: string,
+  draft: { title: string; initialPlan: string },
+  projectId?: string,
+): Promise<{ ok: boolean }> {
+  return api<{ ok: boolean }>(withProjectId(`/ai-sessions/${encodeURIComponent(sessionId)}/draft`, projectId), {
+    method: "PATCH",
+    body: JSON.stringify(draft),
+  });
+}
+
 // ── Messages API ──────────────────────────────────────────────────────────
 
 /** Response shape for GET /messages/inbox */