feat(chat): scope AI conversations to the active project

The chat panel now reads projectId from the URL and tags every thread
to it, so:
- Threads listed in the side panel are filtered to the project the user
  is currently viewing (workspace-level chats still work from /projects).
- New conversations started from a project page are persisted with that
  project_id, surviving page reloads.
- The system prompt prepends an ACTIVE PROJECT block so tool calls
  (apps_create, devcontainer_ensure, etc.) use the right projectId
  without the user having to name it.
- A small chip in the chat header shows which project the AI is
  currently talking about.

Schema migrates idempotently on first request (project_id column +
composite index on fs_chat_threads).

Made-with: Cursor

components/vibn-chat/chat-panel.tsx

@@ -220,6 +220,12 @@ export function ChatPanel() {
   const { data: sessionData, status } = useSession();
   const params = useParams();
   const workspace = (params?.workspace as string) || "";
+  // When the user is on a /project/<id>/* route, scope the chat to
+  // that project. The threads list, the new-thread create call, and
+  // the system prompt all branch on this; the chat header surfaces it
+  // so the user knows the AI is "talking about" the right thing.
+  const projectId = (params?.projectId as string) || "";
+  const [activeProjectName, setActiveProjectName] = useState<string | null>(null);
 
   const [open, setOpen] = useState(() => {
     if (typeof window === "undefined") return false;
@@ -272,29 +278,53 @@ export function ChatPanel() {
       .catch(() => {});
   }, [workspace, status]);
 
-  // Load threads
+  // Load threads (scoped to the current project when one is in the URL).
+  // Reset the loaded flag when projectId changes so the resume effect
+  // re-runs against the correct list and doesn't restore a thread from
+  // the previous project.
   const loadThreads = useCallback(async () => {
     if (!workspace || status !== "authenticated") return;
     try {
-      const res = await fetch(`/api/chat/threads?workspace=${encodeURIComponent(workspace)}`);
+      const qs = new URLSearchParams({ workspace });
+      if (projectId) qs.set("projectId", projectId);
+      const res = await fetch(`/api/chat/threads?${qs.toString()}`);
       const data = await res.json();
       setThreads(data.threads || []);
     } catch { /* silent */ } finally {
       setThreadsLoaded(true);
     }
-  }, [workspace, status]);
+  }, [workspace, projectId, status]);
 
   useEffect(() => {
+    setThreadsLoaded(false);
+    setActiveThread(null);
+    setMessages([]);
     loadThreads();
-  }, [loadThreads]);
+  }, [loadThreads, projectId]);
 
-  // Create and activate a new thread
+  // Look up the active project's display name once we have a projectId,
+  // so the chat header can show "Talking about: <name>".
+  useEffect(() => {
+    if (!projectId) { setActiveProjectName(null); return; }
+    let cancelled = false;
+    fetch(`/api/projects/${projectId}/anatomy`, { credentials: "include" })
+      .then((r) => r.ok ? r.json() : null)
+      .then((d) => {
+        if (cancelled) return;
+        const name = d?.project?.name;
+        if (name) setActiveProjectName(name);
+      })
+      .catch(() => {});
+    return () => { cancelled = true; };
+  }, [projectId]);
+
+  // Create and activate a new thread (tagged to the active project, if any).
   const newThread = useCallback(async () => {
     try {
       const res = await fetch("/api/chat/threads", {
         method: "POST",
         headers: { "Content-Type": "application/json" },
-        body: JSON.stringify({ workspace }),
+        body: JSON.stringify({ workspace, projectId: projectId || undefined }),
       });
       const data = await res.json();
       if (data.thread) {
@@ -304,7 +334,7 @@ export function ChatPanel() {
         setShowThreads(false);
       }
     } catch { /* silent */ }
-  }, [workspace]);
+  }, [workspace, projectId]);
 
   // Load thread messages
   const loadThread = useCallback(async (id: string) => {
@@ -334,18 +364,21 @@ export function ChatPanel() {
       return;
     }
 
-    const savedKey = `vibn-chat-active-thread:${workspace}`;
+    const scopeKey = projectId ? `${workspace}:${projectId}` : workspace;
+    const savedKey = `vibn-chat-active-thread:${scopeKey}`;
     const saved = typeof window !== "undefined" ? localStorage.getItem(savedKey) : null;
     const target = saved && threads.some((t) => t.id === saved) ? saved : threads[0].id;
     loadThread(target);
-  }, [open, status, workspace, threadsLoaded, threads, activeThread, newThread, loadThread]);
+  }, [open, status, workspace, projectId, threadsLoaded, threads, activeThread, newThread, loadThread]);
 
-  // Persist active thread so reload re-opens the same conversation.
+  // Persist active thread so reload re-opens the same conversation,
+  // keyed per-project so each project has its own "last conversation".
   useEffect(() => {
     if (typeof window === "undefined" || !workspace) return;
-    const savedKey = `vibn-chat-active-thread:${workspace}`;
+    const scopeKey = projectId ? `${workspace}:${projectId}` : workspace;
+    const savedKey = `vibn-chat-active-thread:${scopeKey}`;
     if (activeThread) localStorage.setItem(savedKey, activeThread);
-  }, [activeThread, workspace]);
+  }, [activeThread, workspace, projectId]);
 
   useEffect(() => { scrollToBottom(); }, [messages, toolEvents, scrollToBottom]);
 
@@ -583,6 +616,20 @@ export function ChatPanel() {
             transition: "transform 0.15s",
             transform: showThreads ? "rotate(180deg)" : "none",
           }} />
+          {projectId && (
+            <span
+              title={`Chat is scoped to ${activeProjectName ?? "this project"}. Tool calls assume projectId=${projectId}.`}
+              style={{
+                marginLeft: 6, padding: "2px 8px",
+                fontSize: "0.65rem", fontWeight: 600, letterSpacing: "0.02em",
+                color: "#3d5afe", background: "#3d5afe14",
+                borderRadius: 999, maxWidth: 160,
+                whiteSpace: "nowrap", overflow: "hidden", textOverflow: "ellipsis",
+              }}
+            >
+              ▸ {activeProjectName ?? "this project"}
+            </span>
+          )}
         </button>
         <div style={{ display: "flex", gap: 4 }}>
           <button