chore(reusable): bump image pin to sha-5397160 (structured findings contract)

Makes the Phase 1 gadfly-findings contract live for gadfly's own dogfood
reviews (the local-ref reusable). External consumers re-pin separately.

[skip ci]

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/review-reusable.yml

@@ -92,7 +92,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: ${{ inputs.timeout_minutes }}
     steps:
-      - uses: docker://gitea.stevedudenhoeffer.com/steve/gadfly:sha-c342bdb
+      - uses: docker://gitea.stevedudenhoeffer.com/steve/gadfly:sha-5397160
         env:
           # --- event context (from the CALLER's github.*) -------------------
           GITEA_API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}