feat: implement Web Push pipeline for stealth payment alerts

[yustech-alt]

• Add pushRelay.ts library for privacy-first relay integration
• Enhance useNotificationSW.ts hook with subscription management
• Update service workers with push event handling and deduplication
• Add Web Push subscription UI to Settings.tsx
• Implement unsubscribe functionality
• Add privacy protections (meta-address hash only)
• Add comprehensive i18n strings

Closes #158

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[truthixify]

Heads up: this went conflicted a few minutes ago because #168, #169 and #170 landed on develop. It was mergeable right before that, so nothing is wrong with your work.

git fetch origin
git rebase origin/develop

and it should be good to go.

[truthixify]

Rebased onto develop and force-pushed to your branch. Your commits are unchanged.

Single trivial conflict: src/pages/Settings.tsx line 1. develop imports useState, useRef and yours needed useEffect as well, so the resolution is just the union of the two import lists.

Verified locally before pushing: pnpm format:check clean and pnpm build succeeds including the service worker output.

If you have this branch locally, git fetch && git reset --hard origin/web-push-pipeline before continuing.

[truthixify]

Merged @yustech-alt. Self-hostable relay with a user-overridable URL, and dedup against the existing notification history, keeps this privacy-first rather than bolting on a third-party push service. Second one from you this wave.