test(response): fix AbortWithError router tests and oauth/bootstrap reliability

- Add middleware_test.go covering ErrorHandlerMiddleware and Abort helpers
- Switch router test setups to testhelper.NewTestGinEngine for error JSON
- Fix OAuth provider cache to use mock HTTP client and normalize issuer URLs
- Add ResetInitRuntimeOnceForTest to make bootstrap tests hermetic under -count
- Update admin/task test imports for upload/task package move

internal/apps/admin/auth_source/routers_test.go

@@ -19,8 +19,7 @@ import ("bytes"
 	"github.com/Rain-kl/Wavelet/internal/common/response")
 
 func setupTestRouter(authUser *model.User) *gin.Engine {
-	gin.SetMode(gin.TestMode)
-	r := gin.New()
+	r := testhelper.NewTestGinEngine()
 	adminGroup := r.Group("/api/v1/admin")
 
 	// Mock authentication middleware