ci: Friday release train (L1, @chemistry dep-bump)

[vreshch]

Fully automated Friday MINOR release train for @chemistry/molpad (Level 1: releases 1h after the @chemistry base packages at 21:00 Prague).

What this adds

• .github/workflows/release-train.yml - the train:
  • Prague gate: crons 0 19 * * 5 + 0 20 * * 5; proceeds only when TZ=Europe/Prague date +%H == 21 (DST-proof).
  • merge-green-dependabot: chemistry org has no shared triage automation, so the train lists open app/dependabot PRs, polls gh pr checks --json bucket (~10 min max), squash-merges green ones, leaves red open, logs to the step summary.
  • release: bumps internal @chemistry/* deps (npm-check-updates -u --filter '@chemistry/*' + npm install), detects releasable commits, releases if either an internal dep bump or a releasable commit exists (docs/ci/plain-chore excluded; chore(deps) counts). Always a MINOR bump. Runs npm run verify to prove the new base packages integrate, opens + squash-merges the release PR, then dispatches release.yml.
• .github/workflows/release.yml: added a workflow_dispatch path that releases the current package.json version, creating the v<version> tag idempotently (a GITHUB_TOKEN merge never fires the tag-triggered push, so the explicit dispatch is mandatory). Tag-push behavior unchanged.
• .github/dependabot.yml: removed the non-standard major-version ignore rule to match the org standard (weekly Fri 18:00 Europe/Prague, assignees vreshch, groups *, limits 10 npm / 5 github-actions).

Verified locally (in worktree)

• npm ci + ncu @chemistry/* bump (^3.0.0 -> ^3.1.3) + npm install + npm run verify: 270/270 tests pass, build + prettier clean.
• npm version minor --no-git-tag-version -> 3.2.0, stays prettier-clean.
• All 3 YAML files pass python3 yaml.safe_load.

Do not merge yet - awaiting review.

[github-actions]

🎉 PR Validation ✅ PASSED

Commit: 67f0ac4e7d7ff3b5276b31e46857817788d3a708
Branch: ci/friday-release-train

Checks:

• ✅ Dependencies installed
• ✅ Type check passed
• ✅ Linting passed
• ✅ Format check passed
• ✅ Tests passed
• ✅ Build successful

Ready to merge! ✨

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⏰ Generated at: 2026-07-29T23:09:03.008Z