fix(dashboard): fix empty widgets + NULL created_at on campaign tests

1. metrics_query_service: use NULLS LAST in get_recent_tests() so tests
   with actual dates always appear before NULL-dated ones.

2. campaign_service: set created_at=datetime.utcnow() when creating tests
   from campaigns (was missing, leaving 21 tests with NULL created_at).
   Fixed existing NULL values directly in production DB.

3. DashboardPage: add isError handling to all V2 metric widgets
   (pipeline, team activity, validation rate, recent tests).
   - Add retry:2 to all secondary metric queries so transient failures
     are retried before showing empty state.
   - Show 'Could not load X — refresh' instead of empty/misleading
     'No tests created yet' when a query actually fails.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/DashboardPage.tsx

@@ -87,25 +87,29 @@ export default function DashboardPage() {
     queryFn: getCoverageByTactic,
   });
 
-  // V2 queries
-  const { data: pipeline, isLoading: pipelineLoading } = useQuery({
+  // V2 queries — retry:2 so transient failures don't leave widgets blank
+  const { data: pipeline, isLoading: pipelineLoading, isError: pipelineError } = useQuery({
     queryKey: ["metrics", "test-pipeline"],
     queryFn: getTestPipeline,
+    retry: 2,
   });
 
-  const { data: teamActivity, isLoading: teamLoading } = useQuery({
+  const { data: teamActivity, isLoading: teamLoading, isError: teamError } = useQuery({
     queryKey: ["metrics", "team-activity"],
     queryFn: getTeamActivity,
+    retry: 2,
   });
 
-  const { data: validationRates, isLoading: validationLoading } = useQuery({
+  const { data: validationRates, isLoading: validationLoading, isError: validationError } = useQuery({
     queryKey: ["metrics", "validation-rate"],
     queryFn: getValidationRate,
+    retry: 2,
   });
 
-  const { data: recentTests, isLoading: recentLoading } = useQuery({
+  const { data: recentTests, isLoading: recentLoading, isError: recentError } = useQuery({
     queryKey: ["metrics", "recent-tests"],
     queryFn: getRecentTests,
+    retry: 2,
   });
 
   const { data: coverageEvolution, isLoading: evolutionLoading } = useQuery({
@@ -287,6 +291,8 @@ export default function DashboardPage() {
           <div className="flex items-center justify-center py-8">
             <Loader2 className="h-6 w-6 animate-spin text-cyan-400" />
           </div>
+        ) : pipelineError ? (
+          <p className="py-8 text-center text-sm text-gray-500">Could not load pipeline data.</p>
         ) : pipeline ? (
           <PipelineFunnel pipeline={pipeline} />
         ) : null}
@@ -305,6 +311,8 @@ export default function DashboardPage() {
             <div className="flex items-center justify-center py-8">
               <Loader2 className="h-6 w-6 animate-spin text-cyan-400" />
             </div>
+          ) : teamError ? (
+            <p className="py-8 text-center text-sm text-gray-500">Could not load team activity.</p>
           ) : teamActivity ? (
             <div className="space-y-4">
               {teamActivity.map((team: TeamActivityItem) => {
@@ -355,6 +363,8 @@ export default function DashboardPage() {
             <div className="flex items-center justify-center py-8">
               <Loader2 className="h-6 w-6 animate-spin text-cyan-400" />
             </div>
+          ) : validationError ? (
+            <p className="py-8 text-center text-sm text-gray-500">Could not load validation data.</p>
           ) : validationRates ? (
             <div className="space-y-4">
               {validationRates.map((rate: ValidationRateItem) => {
@@ -419,6 +429,8 @@ export default function DashboardPage() {
           <div className="flex items-center justify-center py-8">
             <Loader2 className="h-6 w-6 animate-spin text-cyan-400" />
           </div>
+        ) : recentError ? (
+          <p className="py-8 text-center text-sm text-gray-500">Could not load recent tests — refresh the page.</p>
         ) : recentTests && recentTests.length > 0 ? (
           <div className="overflow-x-auto">
             <table className="w-full text-left text-sm">