feat: implement issues #916, #919, #920, #922

[devJaja]

Summary

Implements four high-priority Stellar Wave issues in a single atomic PR.

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Issue #916 — Advanced search for subscriptions with Elasticsearch

Files changed: backend/elasticsearch/searchService.ts, backend/elasticsearch/__tests__/searchAggregator.test.ts

• SubscriptionSearchAggregator — combines raw Elasticsearch hits with computed facets (category, billing cycle, status) and applies client-side filter sets (price range, tags, status, billing cycle, category).
• SearchFacetManager — stateful filter-toggle manager used by the AdvancedSearchScreen to drive the facet sidebar without re-running full queries.
• SearchAutoComplete — TTL-cached suggestion provider that batches identical prefix requests so the cluster isn't hit on every keystroke.
• ✅ 20 passing tests

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Issue #919 — Batch subscription operations with atomic execution

Files changed: app/services/atomicBatchService.ts, app/screens/BatchOperationsScreen.tsx, contracts/batch/tests/atomic_execution_tests.rs, app/services/__tests__/atomicBatchService.test.ts

• AtomicBatchExecutor — executes ordered subscription operations with snapshot/rollback, idempotency key guard, per-item timeout and a failFast mode that aborts and rolls back on the first failure.
• validateAtomicBatch / deriveIdempotencyKey — pre-flight validation and deterministic key derivation.
• useAtomicBatch — React hook wiring the executor to the existing Zustand batch store.
• AtomicExecutionPanel — new UI component in BatchOperationsScreen showing live status badge, per-item result counts, rollback reason and idempotency key.
• Rust integration tests cover double-execution rejection, rollback-not-allowed for charge ops, and partial-success non-atomic mode.
• ✅ 16 passing tests

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Issue #920 — Subscription notification preferences and management

Files changed: backend/services/notification/preferenceService.ts, src/services/notificationService.ts, backend/services/notification/__tests__/notificationScheduling.test.ts

• DigestNotificationManager — buffers notifications by immediate / daily / weekly frequency and groups flushed batches by channel.
• NotificationScheduler — computes the next delivery timestamp respecting quiet hours and the user's frequency preference.
• NotificationPreferenceSync — change-log with listener callbacks for cross-device preference synchronisation over WebSockets.
• scheduleNotification() — convenience entry-point for the delivery pipeline combining all three services.
• Frontend: getNotificationPreferenceSummary, setAllChannelNotifications, shouldShowNotification added to the React Native notification service.
• ✅ 18 passing tests

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Issue #922 — Payment method management with fallback chains

Files changed: src/services/walletService.ts, src/store/walletStore.ts, src/services/__tests__/fallbackChainHealth.test.ts

• FallbackChainHealthMonitor — computes per-method health snapshots (success rate, avg latency, consecutive failures) within a configurable look-back window and applies rotation policies that automatically promote a healthy backup when the primary degrades.
• SmartFallbackSelector — re-ranks the fallback order by health score and respects active rotation promotions.
• buildFallbackChainDiagnosticReport — human-readable summary for the PaymentMethodsScreen debug panel.
• walletStore extended with getChainHealthSnapshot, getSmartFallbackSelection, getChainDiagnosticReport, full rotation policy CRUD and applyAllRotationPolicies.
• ✅ 15 passing tests

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Testing

Test file	Tests
src/services/__tests__/fallbackChainHealth.test.ts	15 ✅
backend/services/notification/__tests__/notificationScheduling.test.ts	18 ✅
backend/elasticsearch/__tests__/searchAggregator.test.ts	20 ✅
app/services/__tests__/atomicBatchService.test.ts	16 ✅

Total: 69 new tests, all passing.

Closes #916
Closes #919
Closes #920
Closes #922

[drips-wave]

@devJaja Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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