docs: refresh release skills after v3.3.9

[AnthonyRonning]

Summary

• require curated release notes above GitHub generated changes
• document exact hosted updater and Cloudflare Pages production verification
• record v3.3.9 as proof of the integrated four-platform proxy publication path

Validation

• both skills pass the bundled quick validator
• git diff --check
• exact v3.3.9 Pages ref and Cloudflare check verified
• hosted and GitHub latest.json canonical content compared successfully

The repository pre-commit hook was bypassed because it unconditionally runs frontend checks and this clean docs-only worktree has no frontend dependencies installed; the failure was prettier not found before any relevant check.