feat: improve loading and error states on Batch and Analytics pages

Analytics page now shows skeleton loaders (cards and chart placeholders)
while data loads, and displays a retry button when the API call fails.
Batch page error state now shows the actual error message and suggests
user action.

Closes leeworks-agents/SPARC#16

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/Analytics.tsx

@@ -9,15 +9,38 @@ const COLORS = ['#6366f1', '#0ea5e9', '#10b981', '#f59e0b', '#ef4444', '#8b5cf6'
 export function AnalyticsPage() {
   const [days, setDays] = useState(30);
 
-  const { data, isLoading, isError } = useQuery({
+  const { data, isLoading, isError, refetch } = useQuery({
     queryKey: ['analytics', days],
     queryFn: () => analyticsApi.getAnalytics(days),
   });
 
   if (isLoading) {
     return (
-      <div className="flex items-center justify-center min-h-[400px]">
-        <div className="animate-spin rounded-full h-12 w-12 border-t-2 border-b-2 border-primary"></div>
+      <div className="space-y-6">
+        <div>
+          <h2 className="text-xl font-semibold text-text-primary border-b-2 border-primary/30 pb-2 mb-2">
+            Analytics Dashboard
+          </h2>
+          <p className="text-text-secondary">Loading analytics data...</p>
+        </div>
+        {/* Skeleton cards */}
+        <div className="grid grid-cols-1 md:grid-cols-3 gap-4">
+          {[1, 2, 3].map((i) => (
+            <div key={i} className="bg-gradient-to-br from-primary/10 to-secondary/10 border border-primary/20 rounded-xl p-5 text-center animate-pulse">
+              <div className="h-9 w-16 bg-primary/20 rounded mx-auto mb-2" />
+              <div className="h-4 w-24 bg-primary/10 rounded mx-auto" />
+            </div>
+          ))}
+        </div>
+        {/* Skeleton charts */}
+        <div className="grid grid-cols-1 lg:grid-cols-2 gap-6">
+          {[1, 2].map((i) => (
+            <div key={i} className="bg-bg-card/60 border border-primary/15 rounded-2xl p-6 animate-pulse">
+              <div className="h-5 w-40 bg-primary/20 rounded mb-4" />
+              <div className="h-[300px] bg-primary/5 rounded" />
+            </div>
+          ))}
+        </div>
       </div>
     );
   }
@@ -33,15 +56,18 @@ export function AnalyticsPage() {
         <div className="bg-gradient-to-br from-primary/10 to-secondary/5 border border-primary/20 rounded-xl p-6">
           <div className="flex items-center gap-3 text-warning mb-2">
             <Database size={24} />
-            <span className="font-semibold">Database Not Connected</span>
+            <span className="font-semibold">Unable to Load Analytics</span>
           </div>
           <p className="text-text-secondary">
-            Set <code className="bg-bg-card px-2 py-1 rounded">USE_DATABASE=true</code> in your .env file to enable analytics tracking.
+            Could not connect to the analytics database. Ensure PostgreSQL is running and
+            <code className="bg-bg-card px-2 py-1 rounded mx-1">DATABASE_URL</code> is configured correctly.
           </p>
-        </div>
-        <div className="flex items-center gap-2 bg-secondary/10 border border-secondary/20 text-secondary rounded-xl px-4 py-3">
-          <AlertCircle size={18} />
-          <span>Analytics features require storing analysis results in PostgreSQL for historical tracking.</span>
+          <button
+            onClick={() => refetch()}
+            className="mt-3 text-sm bg-primary/20 hover:bg-primary/30 text-primary font-medium px-4 py-2 rounded-lg transition-colors"
+          >
+            Retry
+          </button>
         </div>
       </div>
     );

frontend/src/pages/Batch.tsx

@@ -114,9 +114,21 @@ export function Batch() {
 
       {/* Error */}
       {mutation.isError && (
-        <div className="flex items-center gap-2 bg-error/10 border border-error/20 text-error rounded-xl px-4 py-3">
+        <div className="bg-error/10 border border-error/20 rounded-xl px-4 py-3">
+          <div className="flex items-center gap-2 text-error">
             <AlertCircle size={18} />
-          <span>Batch analysis failed. Please try again.</span>
+            <span className="font-semibold">Batch analysis failed</span>
+          </div>
+          <p className="text-text-secondary text-sm mt-1 ml-7">
+            {mutation.error instanceof Error ? mutation.error.message : 'An unexpected error occurred.'}
+            {' '}Check your connection and try again.
+          </p>
+          <button
+            onClick={() => mutation.reset()}
+            className="ml-7 mt-2 text-sm text-primary hover:text-primary-dark underline"
+          >
+            Dismiss
+          </button>
         </div>
       )}