fix(mobile): add Expo app config for iOS associatedDomains and exampl…

[Davoski1]

Summary

Add iOS associated domains wiring for passkeys and example .well-known payloads for domain association.

Changes

• Add frontend/mobile/app.config.js
  • Dynamic Expo config that injects ios.associatedDomains from EXPO_PUBLIC_PASSKEY_RP_ID (e.g. veil.app or your-domain.com) so the generated iOS build includes webcredentials:<rp-id>.
• Add examples in examples/expo/.well-known/:
  • apple-app-site-association.json — example iOS webcredentials payload for hosting at https://<your-domain>/.well-known/apple-app-site-association.
  • assetlinks.json — example Android Digital Asset Links payload for hosting at https://<your-domain>/.well-known/assetlinks.json.

Why

Mobile passkeys on iOS require the native app entitlement associatedDomains with an entry of the form webcredentials:<rp-id>. This change enables builds to pick the relying-party id from the environment (so secrets/hostnames aren't baked into source) and provides example .well-known payloads that must be hosted on the web origin to complete the platform association.

Notes for maintainers / operators

• Set EXPO_PUBLIC_PASSKEY_RP_ID (e.g. veil.app or your-domain.com) in your CI/EAS or local environment before building iOS artifacts so the entitlement is injected.
• Host apple-app-site-association at https://<domain>/.well-known/apple-app-site-association (the URL typically omits the .json suffix). Serve it over HTTPS with application/json content-type.
• Replace placeholders in the example files:
  • iOS: <TEAM_ID>.<BUNDLE_ID>
  • Android: <your.package.name> and <SHA256> fingerprint(s)

Testing / Verification

1. Build an iOS app with EXPO_PUBLIC_PASSKEY_RP_ID set and verify associatedDomains contains webcredentials:<rp-id> in the generated entitlements.
2. Host apple-app-site-association on the domain and confirm iOS recognizes the association (device logs / Apple verification tools).
3. Verify passkey flows between the domain and the iOS app (registering and using a passkey).

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Closes #446

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[Miracle656]

Thanks for this! It needs a rebase before it can land. Since this branch was opened, the mobile config moved from app.json to app.config.ts, which already sets ios.associatedDomains and android.package (bundle id xyz.veil.wallet). Adding app.config.js here would give Expo two config files.

Could you rebase onto main and fold any still-missing associatedDomains/asset-link changes into the existing app.config.ts (drop the new app.config.js)? Then I'll re-review.