The mobile/ wrapper had 1700+ node_modules files tracked, plus the
Capacitor-regenerated artifacts that get rewritten on every
`npx cap sync android` (capacitor.build.gradle, capacitor.config.json,
capacitor.plugins.json, capacitor.settings.gradle, the cordova-android-
plugins subtree). Every local dev or CI sync caused noisy drift that
blocked scripts/release.sh from running.
Added mobile/.gitignore covering node_modules, cap-sync outputs,
Android build outputs, .jks/.apk/.aab files, and .DS_Store.
Kept package-lock.json tracked for reproducible npm install.
No logic changes — only stopped tracking files that are always
regenerated.