fix: harden cross-platform library query contracts

[zeevenn]

Summary

• enforce stable ID-based cursor, sorting, page-boundary, timestamp, nullable-result, and error contracts across Android and iOS
• prevent non-advancing Android Album and Artist query loops and add complete-library JS helpers used by the example app
• adopt Android content URI-first Track access while retaining compatible url behavior and safe directory filtering
• align the web fallback, public types, English/Chinese documentation, and regression coverage

Verification

• yarn typecheck
• yarn test --runInBand (33 tests)
• yarn lint
• Android unit tests, Kotlin compilation, and lint
• iOS simulator build for arm64 and x86_64
• English and Chinese Docusaurus production builds
• physical-device behavior verified by the maintainer

Closes #13
Closes #14
Closes #17
Closes #20
Closes #21