0.9.50

fix: bump version to 0.9.50 in server.json, constants.ts, logger.ts

Version was stuck at 0.9.38 in:
- server.json (3 occurrences)
- src/core/constants.ts (MCP_SERVER_VERSION)
- src/core/logger.ts (fallback version string)
All now set to 0.9.50 to match package.json and git tag.