Fix Dependabot auto-merge gate to merge only real CI green

[groupthinking]

Update Dependabot auto-merge to classify patch/minor from commit trailers and require all gate-2 check runs to be present and finished before merging.

[linear-code]

GRV-442

[github-actions]

👋 Thanks for opening this issue! It has been automatically labeled for triage.

[groupthinking]

Duplicate of #1476.

That issue described the same two defects — update-type read from a nonexistent dependency.update_type field, and the merge readiness gate reading getCombinedStatusForRef (commit statuses) instead of check runs — and was closed as completed by merged PR #1487, which landed ~15 seconds before this issue was opened.

The current .github/workflows/dependabot-auto-merge.yml on main already does what this issue asks for:

• Update type is parsed from the update-type: trailer in the Dependabot head commit message (the same source dependabot/fetch-metadata reads), allowlisting semver-patch/semver-minor and skipping anything it can't classify.
• The merge job scans checks.listForRef for all gate-2 required check runs, requiring each to be present and completed (not just the combined commit-status surface) before merging.

Closing as a duplicate. If this was filed because the fix hasn't actually taken effect in practice (e.g. DEPENDABOT_AUTO_MERGE_ENABLED behavior), please reopen with details of what's still broken.

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