docs: complete legal credits and notices

[Arbousier1]

What changed

• replaces the broken MahjongCraft link with the actual doublemoon1119/MahjongCraft upstream
• adds complete code, platform, runtime-library, artwork, audio, and trademark credits in both READMEs
• documents Amitaro voice attribution, redistribution limits, terms link, and usage-report requirement
• adds packaged third-party notices, the GB-Mahjong license, resource-pack attribution, and winpthreads notice to release JAR resources

Why

The previous README mixed reference projects with redistributed components and did not make third-party license boundaries or required voice attribution prominent enough. Release JARs also needed self-contained notices.

Impact

No gameplay behavior changes. Users and redistributors get explicit provenance, license boundaries, required credits, and trademark disclaimers; release artifacts retain the relevant notices.

Checks

• git diff --cached --check passed before commit
• local Kotlin/Java compilation, native GB-Mahjong compilation, resource generation, and JAR assembly completed
• full local test execution was interrupted by Windows virtual-memory exhaustion; GitHub Actions is the authoritative clean build for this PR