v1.4-fork-header: fork from message + delete message + header polish + housekeeping

- Fork: POST /api/chats/:id/fork creates a new chat in the same session,
  copies messages up to target (status=complete) with row-offset
  clock_timestamp() for stable ordering. Client emits open_chat_in_active_pane
  event; Workspace opens it in the active pane. No maybeAutoNameChat on forks.
- Delete: DELETE /api/chats/:id/messages/:message_id with 409 if the chat is
  currently streaming. Cascading-forward delete (created_at >= target).
  MessageBubble Trash button + confirm Dialog.
- Header: Projects -> Project -> Session breadcrumb, model badge pill,
  inline session rename, active file path via new useActivePane() hook.
  Server now publishes session_renamed on PATCH /api/sessions/:id;
  client-side dup emit removed from Session.tsx.
- Housekeeping: NOW() -> clock_timestamp() in schema.sql defaults, dead
  PaneTab.tsx and panes/PaneShell.tsx removed, session_panes backfill
  INSERT removed (CREATE TABLE retained), Tailnet trust comment near
  app.listen().

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/hooks/sessionEvents.ts

@@ -57,6 +57,11 @@ export interface AttachChatFileEvent {
   attachment: Omit<Attachment, 'id'>;
 }
 
+export interface OpenChatInActivePaneEvent {
+  type: 'open_chat_in_active_pane';
+  chat_id: string;
+}
+
 export interface SessionArchivedEvent {
   type: 'session_archived';
   session_id: string;
@@ -120,6 +125,7 @@ export type SessionEvent =
   | SessionLoadedEvent
   | OpenFileInBrowserEvent
   | AttachChatFileEvent
+  | OpenChatInActivePaneEvent
   | SessionArchivedEvent
   | ChatCreatedEvent
   | ChatUpdatedEvent