ci: stagger Friday train + dependabot to Etc/UTC

[vreshch]

Summary

• Follow-up to ci: single-workflow Friday train (train.yml) #117: scheduling rules updated estate-wide - no cron at minute :00, and same-host deploy repos stagger 10 min apart (crystallography.io :07, vreshch.com :17, diffractwd.com :27).
• train.yml: cron 0 21 * * 5 -> 27 21 * * 5.
• dependabot.yml: all three ecosystems (npm, docker, github-actions), time: '18:00' / timezone: 'Europe/Prague' -> time: '16:07' / timezone: 'Etc/UTC'. interval/day unchanged.
• This supersedes the SPEC's original "do not touch dependabot.yml" rule, which the coordinator confirmed was revised estate-wide.

Test plan

• YAML parses (yaml.safe_load) for both files
• Diff limited to the intended time/timezone/cron fields only
• PR checks green, then squash-merge

[github-actions]

🎉 PR Validation ✅ PASSED

Commit: aa38910c191e562dfdb0e8ad2f9fc5ed7df01868
Branch: feature/train-v2-stagger

Checks:

• ✅ Dependencies installed
• ✅ Linting passed
• ✅ Format check passed
• ✅ Build successful
• ✅ Docker build
• ✅ E2E tests

Visual Changes: 5 of 20 screenshots changed

📸 downloads dark desktop — 100% changed

📸 downloads dark mobile — 100% changed

📸 downloads light desktop — 100% changed

📸 downloads light mobile — 100% changed

📸 home dark mobile — 1.222% changed

Before	After	Diff

Ready to merge! ✨

---

🔗 View workflow run
⏰ Generated at: 2026-08-10T21:20:07.608Z