fix: Docker container cleanup on session end (Issue #66)

- Added proper SIGTERM/SIGINT signal handlers to stdio-wrapper.ts
- Removed problematic trap commands from docker-entrypoint.sh
- Added STOPSIGNAL directive to Dockerfile for explicit signal handling
- Implemented graceful shutdown in MCP server with database cleanup
- Added stdin close detection for proper cleanup when Claude Desktop closes the pipe
- Containers now properly exit with the --rm flag, preventing accumulation
- Added --init flag to all Docker configuration examples
- Updated documentation with container lifecycle management best practices
- Bumped version to 2.7.20

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Dockerfile

@@ -69,6 +69,9 @@ ENV IS_DOCKER=true
 # Expose HTTP port
 EXPOSE 3000
 
+# Set stop signal to SIGTERM (default, but explicit is better)
+STOPSIGNAL SIGTERM
+
 # Health check
 HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
   CMD curl -f http://127.0.0.1:3000/health || exit 1