governance: centralize release metadata and source reviews

[rwang23]

Summary

• make metadata/release.json the checked source for desktop version, release channel, updater endpoint, capture identity, and capability claims
• require source-art review attestations bound to each original image SHA before rightsVerified is emitted
• generate capability disclosures for the Gallery, Theme Manager, both READMEs, packaged catalog, and release metadata document
• add sanitized bug, performance, accessibility, and compatibility Issue forms
• mark Beta releases as prereleases, enforce tag/version agreement, and keep the updater explicitly unreleased until a signed static all-platform feed exists

Closes #13

Verification

• npm run check
• isolated local-browser QA: Chinese and English Gallery both rendered 68 themes and the generated Windows/macOS capability matrix

Deliberate residuals

• No public signed updater feed is claimed or published by this PR.
• macOS physical Full Skin/persistence verification remains build-only/unverified.
• No release or merge was performed.

[rwang23]

Superseded by #26, now merged into main at e2ed6e8. This branch head is already included in main; closing the draft avoids duplicate review and merge work.