Fix UNIQUE constraint: Use (service_name, version, username) instead of service_fqn

- Change UNIQUE constraint to composite key on separate columns
- Move upsert logic into D1Storage.createService() for atomic operation
- Delete existing service and its offers before inserting new one
- Remove redundant delete logic from app.ts endpoint
- Fixes 'UNIQUE constraint failed: services.service_fqn' error when republishing

src/app.ts

@@ -337,11 +337,7 @@ export function createApp(storage: Storage, config: Config) {
         return c.json({ error: 'Invalid signature for username' }, 403);
       }
 
-      // Delete existing service if one exists (upsert behavior)
-      const existingService = await storage.getServiceByFqn(serviceFqn);
-      if (existingService) {
-        await storage.deleteService(existingService.id, username);
-      }
+      // Note: createService handles upsert behavior (deletes existing service if it exists)
 
       // Validate all offers
       for (const offer of offers) {