Set Up Universal Links / App Links

Background: Native [iOS / Android / both] app. I want links like
[https://example.com/...] to open my app on the right screen, and to fall
back to the web when the app isn't installed.

Use case: Configure verified deep links end to end—the OS association,
not just in-app routing (that's covered by my navigation layer).

Implementation details:
- iOS: Universal Links—the apple-app-site-association (AASA) file, its
  hosting/format, the Associated Domains entitlement, and how the app
  receives the inbound URL. Android: App Links—the assetlinks.json
  Digital Asset Links file, the intent filters with autoVerify, and
  verification.
- The link-pattern → in-app destination mapping (handed to my navigation
  layer from 2.4)
- Cold start vs warm start handling (app launched by the link vs already
  running)
- Web fallback when the app isn't installed
- How to test the verified links on a real device

Deliverable: The full setup checklist per platform (association file +
entitlement/intent filters), the inbound-URL → destination mapping, cold/
warm start handling, and a device test procedure to confirm verification.