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>

src/mcp/server.ts

@@ -2031,4 +2031,18 @@ Full documentation is being prepared. For now, use get_node_essentials for confi
     // Keep the process alive and listening
     process.stdin.resume();
   }
+  
+  async shutdown(): Promise<void> {
+    logger.info('Shutting down MCP server...');
+    
+    // Close database connection if it exists
+    if (this.db) {
+      try {
+        await this.db.close();
+        logger.info('Database connection closed');
+      } catch (error) {
+        logger.error('Error closing database:', error);
+      }
+    }
+  }
 }