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

migrations/fresh_schema.sql

@@ -68,7 +68,7 @@ CREATE TABLE services (
   created_at INTEGER NOT NULL,
   expires_at INTEGER NOT NULL,
   FOREIGN KEY (username) REFERENCES usernames(username) ON DELETE CASCADE,
-  UNIQUE(service_fqn)
+  UNIQUE(service_name, version, username)
 );
 
 CREATE INDEX idx_services_fqn ON services(service_fqn);