Android docs + asset_adapter reference example

[justinjoy]

Parent (umbrella)

#446

Category: Docs
Depends on: #464
Blocking: No
Sizing: M

Deliverable: docs/android.md integration guide (Prefab .aar consumption, JNI_OnLoad skeleton, path handling via Context.getFilesDir(), threading contract, 16KB page alignment, API 21 minimum vs target API floor, NDK version pinning, risks from section 7b.8). examples/android/asset_adapter/ reference AAssetManager-backed adapter demonstrating user_data with captured AAssetManager *, JNI_OnLoad registration, CMakeLists using find_package(wirelog REQUIRED CONFIG).

Files: docs/android.md, examples/android/asset_adapter/asset_adapter.c, .../CMakeLists.txt, .../README.md

Tests: Compile-only check under #465 CI job; no emulator.