feat(mobile-ui): implement skeleton loading states

[Adamskiee]

Summary

• Adds delayed, accessible skeleton loading states across announcements, search, peer profile, profile settings, QR code, and public chat.
• Adds shared skeleton primitives and timing coverage, including overlapping loading cycles.
• Fixes stale peer profile content when a route id changes without an unmount.

Validation

• pnpm run testAll before rebasing onto develop
• pnpm test -- --runInBand app/\(drawer\)/\(tabs\)/peer/__tests__/peer-profile.test.tsx features/shared/hooks/use-delayed-loading.test.ts
• pnpm run typecheck
• pnpm run lint

Smoke test

• Verify slow first loads show one accessible skeleton announcement while cached loads and refetches keep content visible.
• Verify peer A to peer B navigation never shows peer A data on peer B.
• Verify Public Chat and chat detail show unchanged message-bubble skeleton layouts.