feat(changelog): show release time in 12-hour format on whats new page

[parth0025]

What changed

The in-app What's New page now shows each release's publish time in 12-hour format next to the date, e.g. 10 June 2026, 3:59 PM.

• Backend: CHANGELOG.md only records a date, so GET /api/v2/changelog now merges each tag's published_at from the GitHub Releases API. Cached per changelog revision (one API call per new release, not per page view), 10-minute backoff on fetch failure, optional GITHUB_TOKEN support for rate limits.
• Frontend: Changelog.vue renders the date plus 12-hour local time when a timestamp exists, and degrades gracefully to date-only when it does not (e.g. GitHub unreachable).

Verification

• End-to-end check against the real repo: v14.2.0 / v14.1.0 / v14.0.26 all resolve their publish timestamps; the baseline release (no date in CHANGELOG.md) now gains one too
• Controller runtime-loads with STORAGE_TYPE set
• ESLint clean, backend jest suite passes
• Manually tested in browser on the What's New page

🤖 Generated with Claude Code

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