Fix stuck processing jobs and increase timeouts

Background Job Processor:
- Add src/services/jobProcessor.ts that polls RunPod every 30s for stuck jobs
- Automatically completes or fails jobs that were abandoned (user navigated away)
- Times out jobs after 25 minutes

Client-Side Resume:
- Add GET /api/generate/pending endpoint to fetch user's processing jobs
- Add checkPendingJobs() that runs on login/page load
- Show notification banner when user has jobs generating in background
- Add "View Progress" button to resume polling for a job

Timeout Increases (10min → 25min):
- src/utils/validators.ts: request validation max/default
- src/config.ts: RUNPOD_MAX_TIMEOUT_MS default
- public/js/app.js: client-side polling maxTime
- src/services/jobProcessor.ts: background processor timeout

CI/CD Optimization:
- Add paths-ignore to backend build.yaml to skip rebuilds on frontend-only changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/public/css/style.css

@@ -602,6 +602,45 @@ body {
     to { transform: rotate(360deg); }
 }
 
+/* Pending Jobs Banner */
+.pending-jobs-banner {
+    background: linear-gradient(135deg, var(--primary), var(--secondary));
+    color: white;
+    padding: 12px 20px;
+    border-radius: var(--radius);
+    margin-bottom: 20px;
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: 15px;
+    animation: fadeIn 0.3s ease;
+}
+
+.pending-jobs-banner span {
+    font-weight: 500;
+}
+
+.pending-jobs-actions {
+    display: flex;
+    gap: 10px;
+}
+
+.pending-jobs-banner .btn {
+    background: rgba(255, 255, 255, 0.2);
+    border: 1px solid rgba(255, 255, 255, 0.3);
+    color: white;
+    padding: 6px 12px;
+    border-radius: 4px;
+    cursor: pointer;
+    font-size: 12px;
+    font-weight: 500;
+    transition: background 0.2s;
+}
+
+.pending-jobs-banner .btn:hover {
+    background: rgba(255, 255, 255, 0.3);
+}
+
 /* Responsive */
 @media (max-width: 768px) {
     .section-grid {
@@ -621,4 +660,9 @@ body {
     .form-row {
         grid-template-columns: 1fr;
     }
+
+    .pending-jobs-banner {
+        flex-direction: column;
+        text-align: center;
+    }
 }