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/api/client.ts

@@ -148,6 +148,11 @@ export const api = {
         `/api/chats/${chatId}/force_send`,
         { method: 'POST', body: JSON.stringify({ content }) }
       ),
+    fork: (chatId: string, body: { messageId: string; name?: string }) =>
+      request<Chat>(`/api/chats/${chatId}/fork`, {
+        method: 'POST',
+        body: JSON.stringify({ message_id: body.messageId, name: body.name }),
+      }),
   },
 
   messages: {
@@ -166,6 +171,10 @@ export const api = {
         `/api/chats/${chatId}/messages/${messageId}/regenerate`,
         { method: 'POST' }
       ),
+    remove: (chatId: string, messageId: string) =>
+      request<void>(`/api/chats/${chatId}/messages/${messageId}`, {
+        method: 'DELETE',
+      }),
   },
 
   models: () => request<ModelInfo[]>('/api/models'),