fix(test): update API contract tests for new quota fields

Add quota, quota_used, expires_at fields to expected JSON responses
in POST /api/v1/keys and GET /api/v1/keys test cases.

backend/internal/server/api_contract_test.go

@@ -83,6 +83,9 @@ func TestAPIContracts(t *testing.T) {
 					"status": "active",
 					"ip_whitelist": null,
 					"ip_blacklist": null,
+					"quota": 0,
+					"quota_used": 0,
+					"expires_at": null,
 					"created_at": "2025-01-02T03:04:05Z",
 					"updated_at": "2025-01-02T03:04:05Z"
 				}
@@ -119,6 +122,9 @@ func TestAPIContracts(t *testing.T) {
 							"status": "active",
 							"ip_whitelist": null,
 							"ip_blacklist": null,
+							"quota": 0,
+							"quota_used": 0,
+							"expires_at": null,
 							"created_at": "2025-01-02T03:04:05Z",
 							"updated_at": "2025-01-02T03:04:05Z"
 						}