feat(xiaoyunque): add Seedance 2.5

[smackgg]

Summary

• add the first-party XiaoYunque Seedance_2.5 video model and its Convax generation contribution
• expose the model through the companion strict model mapping and package docs
• bump the Plugin to 0.4.3 and companion to 0.3.7 with validation coverage

Validation

• bun run validate -- --kind plugin --id xiaoyunque-generation
• XiaoYunque companion: typecheck, 120 tests, development build, and darwin-arm64 release build passed
• bun run pack -- --kind plugin --id xiaoyunque-generation produced the 0.4.3 package
• repository workspace builds, validation, typechecks, and tests passed; the aggregate local check later stopped in the unrelated cutout-mcp native inference smoke