feat(notifications): add deterministic notification preference handling (#885)

[s6pa1rta3n-lab]

Closes #885

Summary

Implements deterministic notification preference handling with strict account isolation, explicit defaults, offline mutation queueing, and conflict reconciliation.

Acceptance Criteria

• Preferences are isolated by account: Preference states are mapped by normalized account address (account: string), preventing cross-contamination when users switch wallets.
• Defaults are explicit: Frozen default values define all categories (settlement, market, wallet, dispute, payout, system, account) and delivery channels (inApp, email, push).
• Offline changes reconcile without duplication: Offline mutations are queued idempotently and reconciled with remote/server states using deterministic Last-Write-Wins (LWW) timestamp logic.
• Tests cover account switch, conflict, and reset: Comprehensive unit tests cover account switching, conflict resolution, offline queue deduplication, and defaults reset.

Architecture & Implementation

• Type Definitions (types/notification-preferences.ts): Granular types for category toggles, channel toggles, intensity presets, offline mutation records, and reconciliation payloads.
• Preferences Engine (lib/notification-preferences.ts): Immutable explicit defaults, account normalization, defensive deserialization, offline mutation applying, deterministic reconciliation (reconcilePreferences), and decision evaluation (shouldDeliverNotification).
• Scoped Store (app/state/notificationPreferences.ts): Zustand store with persist middleware, cross-tab synchronization via storage event listener, and online/offline event listeners.
• React Hook (hooks/useNotificationPreferences.ts): Auto-synchronizes with WalletContext address changes and exposes helper methods to components.
• Settings UI (app/(dashboard)/settings/page.tsx): Updated settings page to display account-scoped notification preferences, category/channel controls, intensity presets, and one-click "Reset to defaults".

Security and Failure-Mode Considerations

• Account Isolation: Preference lookup strictly normalizes and keys on account identifier, ensuring no leakage of preferences across multiple wallets.
• Defensive Parsing & Fallbacks: Malformed or corrupt storage payloads are caught and populated with valid explicit defaults without throwing runtime exceptions.
• Offline Idempotency: Offline mutations use unique deterministic IDs to prevent duplicate queue items or replay loops.
• Quiet Hours & Critical Alert Bypass: Critical alerts (e.g. disputes, transaction failures) bypass quiet hours suppression to ensure user fund safety.

Verification & Tests

• lib/__tests__/notification-preferences.test.ts: 100% passing tests for normalization, defaults, offline queueing, conflict resolution, and filtering.
• app/state/__tests__/notificationPreferences.test.ts: 100% passing tests for account switching, explicit defaults, reset, offline queueing, and persistence.
• hooks/__tests__/useNotificationPreferences.test.tsx: 100% passing tests for React hook integration and dynamic wallet account switching.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

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