Keep the push subscription open in the Flutter and Android README samples #2101

Tracks PR #2099.

Plan

Goal

Stop the Flutter and Android README Push samples from tearing the subscription down right after subscribing. Copying the current samples calls subscription.unsubscribe() immediately, so no message ever arrives. Raised by Hansi on the README-only SDK PR appwrite/sdk-for-flutter#342 (see also appwrite/sdk-for-android#144).

What changes

• PR #2099 (docs/readme-review-fixes):
  • templates/flutter/README.md.twig: drops the trailing subscription.unsubscribe(); from the Push sample and adds a sentence to keep subscription while you want messages and unsubscribe when you stop listening, for example in the widget's dispose().
  • templates/android/README.md.twig: same change for the Kotlin sample, pointing at the activity's onDestroy().

Remaining steps

None in the generator. PR #2099 is the full template change. The generated READMEs reach appwrite/sdk-for-flutter and appwrite/sdk-for-android with their next SDK regeneration (the open README PRs there may need the same edit).

Done when

• PR docs(flutter,android): keep the push subscription open in README samples #2099 is merged
• php example.php flutter client and php example.php android client generate Push sections that keep the subscription open
• The Flutter and Android SDK READMEs carry the corrected samples