perf(android): reduce apk size from 70MB to 6.7MB

[gmegidish]

Cuts the Android APK from 70MB (debug) to 6.7MB (signed release).

• Removed material-icons-extended (~40MB of dex); all 5 icons used come from the core set bundled with Material3
• Enabled R8 minification for release, signed with debug keystore so it installs anywhere
• hero_foreground: 3MB PNG → 413KB WebP; launcher icons resized per density bucket (were 1024×1024 in all 5); adaptive icon background 550KB → 44KB
• make apk now builds the signed release and outputs apk/release/Milliways.apk

https://claude.ai/code/session_017uxY2rko33BrcwiYdTP9fg