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/cap/routers_test.go

@@ -23,8 +23,7 @@ func TestCapEndpointsAndMiddleware(t *testing.T) {
 	sqliteDB, _, cleanup := testhelper.SetupTestEnvironment(t)
 	defer cleanup()
 
-	gin.SetMode(gin.TestMode)
-	r := gin.New()
+	r := testhelper.NewTestGinEngine()
 
 	// Mount CAPTCHA API endpoints
 	capGroup := r.Group("/api/cap")