Automate Code Signing

Background: Native [iOS / Android] app. Code signing today: [manual /
broken / not set up]. Team: [solo / multiple devs / CI needs to sign].

Use case: Get code signing automated and reproducible so it works the
same on my machine and in CI—this is the part that breaks most often.

Implementation details:
- iOS: explain certificates vs provisioning profiles vs the App ID, and
  set up a managed approach (Fastlane match with a shared encrypted repo,
  or Xcode Cloud's managed signing). Cover distribution vs development
  profiles and how CI gets the credentials securely.
- Android: keystore creation and safekeeping, the signing config, and
  Play App Signing (Google holds the app signing key, you hold the
  upload key)—explain the distinction.
- Never commit signing material; inject via CI secrets
- A recovery plan if a key/cert is lost or expires

Deliverable: The signing setup for my platform (managed approach +
CI-secret injection), an explanation of the certificate/profile or
keystore/Play-signing model, and the recovery plan for lost/expired
credentials.