fix(ci): re-pin titus-scan to real tag v2.6.0 + adopt verify-pins gate

[nsportsman]

Why

Two pin-integrity fixes, in one PR per repo:

1. Re-pin titus-scan to a real tag. This repo pinned the Titus secret-scanner
   reusable with the comment # v2.2.1 — but that tag never existed (public-workflows
   tags jump v2.2.0 → v2.3.0). A lying version comment defeats audits and Dependabot.
   Re-pinned to v2.6.0 (23254e12b026), the current tag carrying the hardened,
   fail-closed, visibility-aware titus-scan reusable. Byte-identical scanner behavior —
   this is a label-honesty fix.

2. Adopt the verify-pins gate. Adds .github/workflows/verify-pins.yml calling the
   new reusable (also v2.6.0). On any future .github/workflows/** change it verifies
   every first-party public-workflows pin's # vX.Y.Z comment matches a real tag at that
   SHA — so a dishonest pin can never merge again.

All other first-party pins in this repo (go-ci, codex-code, claude-code, gemini-code,
claude-md-drift, external-contrib, go-sec) were audited and are already honest, so the new
gate passes on this PR.

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: e4f3cc80-20a9-4985-893a-14d54cff4c41

📥 Commits

Reviewing files that changed from the base of the PR and between a54c925 and 769fc55.

📒 Files selected for processing (2)

• .github/workflows/secrets-scan.yml
• .github/workflows/verify-pins.yml

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/repin-titus-v2.6.0-and-verify-pins

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[github-actions]

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