* chore: set all Dependabot update intervals to monthly

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* chore: point Dependabot gradle ecosystem at the android project

The gradle entry's directory: "/" scanned the repo root, but there is
no build.gradle(.kts) there — the three Gradle build files live at
android/build.gradle.kts, android/app/build.gradle.kts, and
android/googlepay/build.gradle.kts. Replace the single root directory
with a directories list covering /android, /android/app, and
/android/googlepay so Dependabot actually scans the Gradle projects.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>