feat(parcel-sync): incremental sync, smart export, auto-refresh + weekend deep sync

Sync Incremental:
- Add fetchObjectIds (returnIdsOnly) to eterra-client — fetches only OBJECTIDs in 1 request
- Add fetchFeaturesByObjectIds — downloads only delta features by OBJECTID IN (...)
- Rewrite syncLayer: compare remote IDs vs local, download only new features
- Fallback to full sync for first sync, forceFullSync, or delta > 50%
- Reduces sync time from ~10 min to ~5-10s for typical updates

Smart Export Tab:
- Hero buttons detect DB freshness — use export-local (instant) when data is fresh
- Dynamic subtitles: "Din DB (sync acum Xh)" / "Sync incremental" / "Sync complet"
- Re-sync link when data is fresh but user wants forced refresh
- Removed duplicate "Descarca din DB" buttons from background section

Auto-Refresh Scheduler:
- Self-contained timer via instrumentation.ts (Next.js startup hook)
- Weekday 1-5 AM: incremental refresh for existing UATs in DB
- Staggered processing with random delays between UATs
- Health check before processing, respects eTerra maintenance

Weekend Deep Sync:
- Full Magic processing for 9 large municipalities (Cluj, Bistrita, TgMures, etc.)
- Runs Fri/Sat/Sun 23:00-04:00, round-robin intercalated between cities
- 4 steps per city: sync terenuri, sync cladiri, import no-geom, enrichment
- State persisted in KeyValueStore — survives restarts, continues across nights
- Email status report at end of each session via Brevo SMTP
- Admin page at /wds: add/remove cities, view progress, reset
- Hint link on export tab pointing to /wds

API endpoints:
- POST /api/eterra/auto-refresh — N8N-compatible cron endpoint (Bearer token auth)
- GET/POST /api/eterra/weekend-sync — queue management for /wds page

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

src/instrumentation.ts

@@ -0,0 +1,11 @@
+/**
+ * Next.js instrumentation hook — runs once at server startup.
+ * Used to initialize background schedulers.
+ */
+export async function register() {
+  // Only run on the server (not during build or in edge runtime)
+  if (process.env.NEXT_RUNTIME === "nodejs") {
+    // Start the ParcelSync auto-refresh scheduler (side-effect import)
+    await import("@/modules/parcel-sync/services/auto-refresh-scheduler");
+  }
+}