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/server/src/schema.sql

@@ -2,7 +2,7 @@ CREATE TABLE IF NOT EXISTS projects (
   id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
   name TEXT NOT NULL,
   path TEXT NOT NULL UNIQUE,
-  added_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  added_at TIMESTAMPTZ NOT NULL DEFAULT clock_timestamp(),
   last_session_id UUID
 );
 
@@ -12,8 +12,8 @@ CREATE TABLE IF NOT EXISTS sessions (
   name TEXT NOT NULL,
   model TEXT NOT NULL,
   system_prompt TEXT NOT NULL DEFAULT '',
-  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
-  updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+  created_at TIMESTAMPTZ NOT NULL DEFAULT clock_timestamp(),
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT clock_timestamp()
 );
 
 CREATE INDEX IF NOT EXISTS idx_sessions_project ON sessions(project_id, updated_at DESC);
@@ -27,7 +27,7 @@ CREATE TABLE IF NOT EXISTS messages (
   tool_results JSONB,
   status TEXT NOT NULL DEFAULT 'complete',
   last_seq INT NOT NULL DEFAULT 0,
-  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+  created_at TIMESTAMPTZ NOT NULL DEFAULT clock_timestamp()
 );
 
 CREATE INDEX IF NOT EXISTS idx_messages_session ON messages(session_id, created_at);
@@ -60,14 +60,9 @@ CREATE TABLE IF NOT EXISTS session_panes (
 );
 CREATE INDEX IF NOT EXISTS idx_session_panes_session ON session_panes (session_id);
 
--- Backfill: ensure every session has at least one pane (default Chat).
--- Idempotent: skipped on subsequent runs because session_panes rows already exist.
-INSERT INTO session_panes (session_id, position, kind, state)
-SELECT s.id, 0, 'chat', '{}'::jsonb
-FROM sessions s
-WHERE NOT EXISTS (
-  SELECT 1 FROM session_panes p WHERE p.session_id = s.id
-);
+-- v1.4: backfill removed. Pane layout is client-side (localStorage) since v1.2-batch4.
+-- The CREATE TABLE above is retained for additive-schema discipline; drop is a
+-- future destructive migration.
 
 -- v1.2: sessions.status (open | archived)
 ALTER TABLE sessions ADD COLUMN IF NOT EXISTS status TEXT NOT NULL DEFAULT 'open';