fix: add missing stop_force and store_force helpers

## Fix missing `stop_force` and `store_force` helpers This PR fixes [#194](https://github.com/GaiaNet-AI/gaianet-node/issues/194). ### Problem The script called `stop_force` and `store_force` inside `start_chat_server()`, but neither function was defined. This caused crashes such as: /home/viperx808/gaianet/bin/gaianet: line 588: store_force: command not found ### Solution - Added `stop_force()` to safely kill any leftover `wasmedge` process and remove stale PID files. - Added `store_force()` to preserve chat server logs with timestamping, preventing data loss. ### Testing - Ran `gaianet-node start --log_level=debug` locally. - Script no longer fails at line 588. - Verified that logs are properly preserved and server shutdowns are safe. --- ✅ This makes the node startup more stable and prevents unrecoverable crashes.