labelle.games v2: Android companion app (silent auto-update)

[apotema]

Part of #139 (labelle.games platform).

Scope

Lightweight Android app (~2MB) that testers install once:

1. Tester opens https://labelle.games/t/<project>/<channel> on their device
2. Web page guides them to install the companion app
3. Companion app registers the device with labelle.games
4. Downloads and installs the game APK
5. On new versions: silent auto-update via Android PackageInstaller API
6. Shows notification when new version is ready to play

Features

• Poll for updates on schedule (configurable interval)
• Support multiple projects/channels per device
• Minimal permissions (install packages, network, notifications)
• No game-specific code — generic for any labelle project

Tech

• Kotlin (minimal native app) or Flutter
• PackageInstaller API for silent install (requires user opt-in on first install)

Acceptance

• Tester opens link → installs companion → gets game automatically
• Developer pushes new version → tester's tablet updates within minutes

[apotema]

Deferred to v2 per the pivot proposed in #139 (Obtainium + GitHub Releases for v1). The Android companion app (silent auto-update) becomes relevant once we outgrow Obtainium's self-serve subscription model — see #139 for the v2 triggers. Leaving this open as the v2 spec.