feat(ProcessManager): add Bun availability check and improve PID file validation

- Implemented a method to check if Bun is available in the system PATH.
- Updated the startWithBun method to return an error if Bun is not found.
- Enhanced PID file parsing to validate required fields and their types.
- Cleaned up stale PID files if the process is no longer alive.

fix(SettingsRoutes): clear port cache after updating settings

- Added a call to clearPortCache after writing updated settings to ensure the application uses the latest configuration.

docs/public/usage/search-tools.mdx

@@ -364,7 +364,7 @@ search_sessions with query="[YOUR PROJECT NAME]" and orderBy="date_desc"
 If search isn't working, check the worker service:
 
 ```bash
-pm2 list                    # Check worker status
+npm run worker:status       # Check worker status
 npm run worker:restart      # Restart if needed
 npm run worker:logs         # View logs
 ```