feat: add legal pages and review prompt

[markm39]

Summary

• add public GitHub Pages legal/support pages for OpenNotes
• link Privacy, Terms, and Support from the in-app About sheet
• add a local-only native store review prompt after positive usage moments
• install expo-store-review and refresh iOS Pods

Review prompt timing

The app records local-only engagement signals for note creation, note opens, successful saves, and exports. It requests the native store review dialog only after a positive moment on library focus, with minimum use thresholds, a 15-minute first-use guard, a 120-day cooldown, and a max of 3 prompts.

Verification

• npm run typecheck
• npx expo config --type public
• pod install
• git diff --check
• npm audit --omit=dev --audit-level=high
• curl verified published GitHub Pages privacy, terms, and support URLs return 200

Notes

• GitHub Pages is already published from the gh-pages branch so the store URLs are live now.
• npm audit still reports moderate Expo/PostCSS advisories that require a breaking Expo major upgrade to auto-fix.