ci(android): dockerfile for reproducible APK builds

[mickenordin]

Summary

• Add Dockerfile.android, mirroring Dockerfile.deb / Dockerfile.rpm / Dockerfile.arch so APK builds are reproducible without installing the Android toolchain on the host.
• Debian 13 base; JDK 21; Node 22; pnpm; Rust with aarch64-linux-android, armv7-linux-androideabi, i686-linux-android, x86_64-linux-android targets.
• Pins Android cmdline-tools 11076708, platform android-34, build-tools 34.0.0, NDK 27.0.12077973.
• Symlinks target-prefixed ar / ranlib / strip / nm in the NDK toolchain bin so the vendored openssl-sys build (which calls aarch64-linux-android-ranlib etc.) completes on recent NDKs that only ship the generic llvm-* names.
• Build produces a debug-signed universal APK and copies it to /out on docker run.

Usage:

docker build -f Dockerfile.android -t chithi-android .
mkdir -p out && docker run --rm -v "$PWD/out:/out" chithi-android
adb install -r out/app-universal-debug.apk

Note: building on main requires src-tauri/gen/android/ to exist. It lands with the mobile branch (#112). This Dockerfile is useful as-is against that branch; against plain main the build will fail until the mobile scaffold is merged.

Test plan

• Builds the image end-to-end on my machine (Debian 14 host).
• Produces out/app-universal-debug.apk.
• adb install -r onto a physical device; app launches.