refactor: rename update-machine-metadata to update-machine

- Consistent naming with the update body type (t: 'update-machine')
- Shorter and cleaner event name
- Matches the pattern used elsewhere in the codebase

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

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

sources/app/api.ts

@@ -1531,8 +1531,8 @@ export async function startApi(): Promise<{ app: FastifyInstance; io: Server }>
             }
         });
 
-        // Update machine metadata through socket
-        socket.on('update-machine-metadata', async (data: { metadata: string }) => {
+        // Update machine through socket
+        socket.on('update-machine', async (data: { metadata: string }) => {
             if (connection.connectionType !== 'machine-scoped') {
                 return; // Only machines can update their own metadata
             }