Builds the signed release AAB for a Mob Android app.

Called by mix mob.release --android. The pipeline:

1. Download the Android OTP runtime (arm64) if not already cached.
2. Copy the OTP tree to a temp staging dir and add:
   • App + dep BEAMs (flattened into {app_name}/)
   • App priv/ → {app_name}/priv/
   • exqlite BEAMs → lib/exqlite-{vsn}/ebin/ (OTP lib structure needed for :code.lib_dir(:exqlite) to resolve correctly at runtime)
3. Run MobDev.OtpAssetBundle.build/2 — strips unused OTP libs and optional BEAM chunks, then zips the tree to src/release/assets/otp.zip.
4. Run ./gradlew bundleRelease — signs the AAB using the keystore configured in android/keystore.properties.

MobBridge.extractOtpIfNeeded() (Kotlin) extracts otp.zip into <filesDir>/otp/ on first launch. Without this zip the app crashes immediately — the BEAM has no runtime or application BEAMs to load.

The zip is written to the release-variant asset source set, not the shared main one — Gradle only merges src/release/assets/ into release builds, so a leftover zip from a prior release build can never leak into (and silently poison) a subsequent debug build. See decisions/2026-07-24-release-otp-zip-variant-scoped-assets.md.