chore(public): align repository hygiene and checks

[Codewriter90x]

Summary

• align public documentation, support guidance, release checklists, and CODEOWNERS with the repository's current public state;
• refresh the verified dependency inventory and correct gameplay-theme instructions;
• improve first-visit language selection and image dimensions on the website;
• add a macOS CI job that builds and exercises the native CoreMIDI plug-in.

Why

The source-only launch left several preparation-era statements and dependency
versions behind. The website also defaulted every new visitor to Italian, and
the native C++ boundary was not exercised by public CI.

Validation

• public-readiness contracts: passed;
• asset-provenance contracts: passed (63 assets);
• macOS signing foundation contracts: passed;
• Windows packaging contracts: passed;
• CoreMIDI arm64 build and native tests: passed;
• workflow YAML and website JavaScript syntax: passed;
• rendered website QA: desktop and mobile passed, language switch persisted,
  mobile navigation worked, and no console errors were observed;
• full .NET tests: delegated to GitHub CI because the exact SDK 8.0.411 is not
  installed in the local audit environment.

Scope

No Unity player binary, commercial content, gameplay feature, scoring,
persistence, web backend, or AI functionality is added.