feat: add API token authentication (closes #87)

- Add api_tokens table migration (007)
- Add APIToken model with CRUD operations
- Generate tokens with upaas_ prefix + 32 hex chars
- Store SHA-256 hash of tokens (not plaintext)
- Update APISessionAuth middleware to check Bearer tokens
- Add POST/GET/DELETE /api/v1/tokens endpoints
- Token creation returns plaintext once; list never exposes it
- Expired and revoked tokens are rejected
- Tests for creation, listing, deletion, bearer auth, revocation

internal/server/routes.go

@@ -119,6 +119,11 @@ func (s *Server) SetupRoutes() {
 			r.Delete("/apps/{id}", s.handlers.HandleAPIDeleteApp())
 			r.Post("/apps/{id}/deploy", s.handlers.HandleAPITriggerDeploy())
 			r.Get("/apps/{id}/deployments", s.handlers.HandleAPIListDeployments())
+
+			// API token management
+			r.Post("/tokens", s.handlers.HandleAPICreateToken())
+			r.Get("/tokens", s.handlers.HandleAPIListTokens())
+			r.Delete("/tokens/{tokenID}", s.handlers.HandleAPIDeleteToken())
 		})
 	})