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/src/config.ts

@@ -64,7 +64,7 @@ export const config = {
     endpointId: requireEnv('RUNPOD_ENDPOINT_ID'),
     baseUrl: 'https://api.runpod.ai/v2',
     pollIntervalMs: optionalEnvInt('RUNPOD_POLL_INTERVAL_MS', 5000),
-    maxTimeoutMs: optionalEnvInt('RUNPOD_MAX_TIMEOUT_MS', 600000),
+    maxTimeoutMs: optionalEnvInt('RUNPOD_MAX_TIMEOUT_MS', 1500000),
   },
 
   // WebAuthn