feat(pwa): wire offline payment queueing into send flow, fix install/sync bugs

[TheWeirdDee]

Summary

Closes #388.

This repo's main already carries PWA install-prompt and offline-queue infrastructure merged from earlier issues (#380, #358, #24) — InstallPrompt.tsx, lib/offlineQueue.ts, lib/cacheData.ts, and hooks/useNetworkStatus.ts all predate this PR. What was still missing against #388's acceptance criteria was wiring that infrastructure into the actual payment flow and fixing a few bugs left over from that work:

• SendPaymentForm now actually calls queueTransaction() when a signed payment is submitted while offline, instead of just letting the submission fail.
• dashboard.tsx balance fetch now reads/writes through cacheData.ts (IndexedDB) in addition to the existing localStorage snapshot, so the offline banner has a real synced timestamp to show.
• New QueueSyncNotifier component toasts the result of each queued transaction once connectivity returns and the queue drains (success/failure per payment), listening both to the in-page processQueue() path and the service worker's QUEUE_PROCESSED message.
• InstallPrompt's install-event tracking previously dispatched a CustomEvent with no listener anywhere, so "installation events are tracked" wasn't actually true — now routed through the app's existing Plausible-based analytics convention (matches lib/onboardingState.ts's trackOnboardingEvent).
• OfflineBanner now consumes the useNetworkStatus hook (previously created per spec but never imported anywhere) instead of duplicating its own online/offline listeners.
• Fixed a queue-processing race: _app.tsx was calling attachOnlineListener() on mount, which registers a second online listener that independently calls processQueue(). Since OfflineBanner (mounted app-wide) already reacts to the same event via Background Sync or its own processQueue() fallback, two listeners could race against the same IndexedDB queue on reconnect — in the worst case double-submitting a queued payment, or causing a successful submission to get mislabeled "failed" when the losing racer's resubmission is rejected by Horizon for a stale sequence number. Removed the redundant call; OfflineBanner already owns this correctly.
• Service worker is now registered unconditionally on app load (_app.tsx) rather than only on-demand via the push-notification opt-in flow, so install eligibility and offline caching are available from first load.

Test plan

• npx tsc --noEmit — no new errors introduced (diffed against clean main baseline; all remaining errors are pre-existing and unrelated)
• npx eslint on all touched files — clean
• __tests__/offlineQueue.test.ts — passes (one attachOnlineListener test is flaky on clean main too, unrelated to this change)
• Manual verification of install prompt / offline banner / queue sync UI in a browser (not run in this environment)

[TheWeirdDee]

Closing — opened with unwanted AI-attribution text in the description that the author did not approve.

[github-actions]

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