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

[s6pa1rta3n-lab]

Closes #885

Summary & Motivation

Users need predictable, robust, and deterministic control over settlement, market, wallet, and dispute notifications. This PR introduces an account-scoped notification preferences subsystem with explicit defaults, conflict resolution, offline reconciliation, and UI controls.

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Acceptance Criteria Checklist

• Preferences are isolated by account: Stored in useNotificationPreferencesStore keyed by normalized account ID (e.g. Stellar address or normalized anonymous). Switching accounts immediately rebinds preferences and isolates custom settings without cross-contamination (app/state/notificationPreferences.ts, hooks/useNotificationPreferences.ts).
• Defaults are explicit: DEFAULT_NOTIFICATION_PREFERENCES provides explicit immutable defaults (intensity: important, default channels: inApp: true, categories: all high-signal enabled, quiet hours configured) with isDefault status checking (lib/notification-preferences.ts, types/notification-preferences.ts).
• Offline changes reconcile without duplication: applyOfflineMutation and reconcilePreferences provide deterministic Last-Write-Wins (LWW) resolution and monotonic versioning with mutation deduplication tracking (lib/notification-preferences.ts, app/state/notificationPreferences.ts).
• Tests cover account switch, conflict, and reset: Unit and integration test suites comprehensively verify account switching, LWW conflict reconciliation, offline queues, default reset, and filtering logic (lib/__tests__/notification-preferences.test.ts, app/state/__tests__/notificationPreferences.test.ts, hooks/__tests__/useNotificationPreferences.test.tsx).

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Implementation Details

• Schema & Types (types/notification-preferences.ts): Typed definitions for notification categories (settlement, market, wallet, dispute, payout, system, account), delivery channels (inApp, email, push), intensity profiles (important, balanced, everything), quiet hours, and mutation records.
• Core Engine & Reconciliation (lib/notification-preferences.ts): Deterministic pure functions for normalization, cloning, validation, offline mutations, LWW reconciliation, and notification filtering (shouldDeliverNotification).
• Store & Cross-Tab Sync (app/state/notificationPreferences.ts): Account-scoped Zustand store using persist middleware, offline network listeners, and cross-tab storage synchronization.
• React Hook (hooks/useNotificationPreferences.ts): React hook binding active wallet address to scoped notification preferences with ergonomic setters and reset capabilities.
• Settings UI (app/(dashboard)/settings/page.tsx): Dedicated Notifications tab with granular category and channel switches, intensity presets, active account indicators, and default reset actions.

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Security & Failure-Mode Considerations

1. Account Isolation: Account keys are defensively normalized (lowercased/trimmed) to prevent casing mismatches and leakage across sessions.
2. Offline Resilience: Offline mutations record unique IDs and timestamps so network drops or reconnects reconcile without dropping user intent or causing race conditions.
3. Safe Defaults: High-signal alerts (settlement, dispute, wallet) are enabled by default while noisy market updates are throttled under the important preset.

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Payout Routing

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

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