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/components/panes/PaneShell.tsx

@@ -1,31 +0,0 @@
-import type { ReactNode } from 'react';
-import type { Pane } from '@/api/types';
-import { X } from 'lucide-react';
-import { cn } from '@/lib/utils';
-
-interface Props {
-  pane: Pane;
-  onClose: () => void;
-  className?: string;
-  children: ReactNode;
-}
-
-export function PaneShell({ pane, onClose, className, children }: Props) {
-  const label = pane.kind === 'chat' ? 'Chat' : 'Files';
-  return (
-    <div className={cn('flex flex-col h-full min-h-0 border-r border-border last:border-r-0', className)}>
-      <div className="flex items-center justify-between px-3 py-1.5 border-b border-border bg-muted/30">
-        <span className="text-xs font-medium text-muted-foreground">{label}</span>
-        <button
-          type="button"
-          onClick={onClose}
-          className="p-0.5 hover:bg-muted rounded"
-          aria-label="Close pane"
-        >
-          <X size={12} />
-        </button>
-      </div>
-      <div className="flex-1 min-h-0 overflow-hidden">{children}</div>
-    </div>
-  );
-}