ci: repin orphan rust-ci-reusable SHA (4fdf4314 → cc5a372a) (#247)

## Summary

`.github/workflows/rust-ci.yml` pinned
`hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@4fdf4314`
— an orphan SHA (not reachable from `standards/main`). Read-only
Contents API still resolves the blob (cached), so code-review does not
catch this, but `workflow_call` at run-time refuses orphan SHAs and
emits "workflow file issue" with zero jobs created.

## Fix

Re-pin to the reachable merge-commit SHA
`cc5a372af1af1b202c17f1b21efd954e6c038bef` (#299, the latest commit
touching the reusable).

## Reference

- Audit:
hyperpolymath/standards/docs/audits/audit-hypatia-pin-orphan-2026-05-27.adoc
- Detector: hypatia rule WF016
(`Hypatia.Rules.WorkflowAudit.check_orphan_standards_reusable_pin`,
added hyperpolymath/hypatia#393)

## Estate-wide impact

This is one of ~83 repos pinning this orphan rust-ci-reusable SHA.
Parallel pattern: ~95 repos pinning orphan hypatia-scan-reusable SHA
`@97df7621` → `@915139d7`. Combined ~178-repo fan-out tracked under
hyperpolymath/standards#282 (or a follow-up issue).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/rust-ci.yml

@@ -14,7 +14,7 @@ permissions:
 
 jobs:
   rust-ci:
-    uses: hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@4fdf4314b4ab54269adbaff10e30e483b5e86845
+    uses: hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@cc5a372af1af1b202c17f1b21efd954e6c038bef
 
   no-default-features:
     name: Cargo build + test (ephapax-cli, --no-default-features)