Run required checks for merge-queue groups #523

Problem

The branch rules require Conventional Commit Title, Python Lint & Test, and Pattern Validation. Their workflows trigger on pull_request but not merge_group, so a queued PR waits forever for checks that never start on the merge-group SHA. Observed on #522 at merge-group commit 1dd4090d53a565242cda635ec8e3dcaf5935b017.

Scope

• Add merge_group triggers for main to the workflows that own all required contexts.
• Preserve pull-request semantic-title validation.
• Ensure the identically named Conventional Commit Title context reports success on merge groups without trying to read unavailable PR event fields.
• Keep permissions least-privileged and actions pinned.

Acceptance criteria

• All three required contexts run on a merge-group SHA.
• Pull-request title validation remains unchanged.
• Workflow syntax/security validation passes.
• A PR successfully progresses through the merge queue after this fix merges.

Relationships

Unblocks: #522.
Related epic: #357.

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