Force terminal redraw on reconnect

- Track last known terminal size in TerminalSession
- Add force_redraw() method that re-sends SIGWINCH to trigger redraw
- Call force_redraw() when WebSocket reconnects to existing session
- Helps tmux and similar apps restore proper display after disconnect

src/textual_webterm/local_server.py

@@ -445,6 +445,9 @@ class LocalServer:
             if session is None or not session.is_running():
                 self.session_manager.on_session_end(session_id)
                 session_id = None
+            elif hasattr(session, "force_redraw"):
+                # Force redraw on reconnect to refresh tmux/screen displays
+                await session.force_redraw()
 
         session_created = session_id is not None