fix(terminal): refactor WebSocket cleanup, buffer management, and disposal

- Add proper disposal tracking to prevent memory leaks
- Move terminal buffer from localStorage to sessionStorage
- Restore buffer immediately after first WS message
- Fix clear detection logic and error handling
- Add signal parameter support for abortable fetch requests

💘 Generated with Crush

Assisted-by: MiniMax-M2.7 via Crush <crush@charm.land>

internal/api/terminal.go

@@ -165,8 +165,6 @@ func (s *Server) handleTerminalWS(w http.ResponseWriter, r *http.Request) {
 			n, err := ptmx.Read(buf)
 			if err != nil {
 				cleanup()
-				conn.WriteMessage(websocket.CloseMessage,
-					websocket.FormatCloseMessage(websocket.CloseNormalClosure, ""))
 				return
 			}
 			if err := conn.WriteJSON(wsMessage{