feat(android): ship mobile ink v1 parity

[markm39]

Summary

• add the Android native MobileInkCanvasView, module, package, Gradle/CMake wiring, and example docs
• render Android with TextureView + EGL + Skia Ganesh so drawing stays GPU-backed like iOS
• bring continuous-page behavior to parity: pooled page activation, trailing blank-page growth, dirty-page capture, previews while engines mount, and autosave status in the example
• fix Android color ordering for live Ganesh rendering, previews, and PDF-backed pages
• split the larger C++ drawing implementation into focused rendering, eraser, history, selection, crayon, calligraphy, and shape-recognition modules

Android v1 Scope

This PR is the Android v1 implementation for mobile-ink: drawing, erasing, selection chrome, multiple pages, page previews during engine load, persisted notebook reloads, and example Android run docs.

Not in this Android v1 PR: Android native benchmark runner UI/API. The example keeps benchmark controls iOS-only until the Android recorder/runner lands.

Validation

• npm run typecheck
• npm test
• npm run test:native:smoke
• npm run test:example:typecheck
• ./gradlew ':mathnotes_mobile-ink:compileDebugKotlin' :app:assembleDebug
• Manual Android device validation by Mark: drawing, multi-page activation, eraser, and color ordering are working

Review Gates

• simplify: no blocking maintainability findings after review
• security: no auth, tenant isolation, secret, injection, or sensitive-data findings in this native/client-only surface