Update tooling dependencies (March 2026) (#307)

## Summary

Monthly tooling dependency update per [[update-tooling-dependencies]].

- **Prek hooks:** trufflehog v3.93.4→v3.94.0, ruff v0.15.2→v0.15.7, shfmt v3.12.0-2→v3.13.0-1, ansible-lint floor→26.3.0, ansible-core floor→2.18
- **Fly.io proxy:** nginx 1.28.2→1.29.6, Grafana Alloy v1.13.1→v1.14.1
- **Forgejo workflows:** actions/checkout v4.3.1→v6.0.2 (SHA-pinned across all 5 workflows)
- **Mise tasks:** tightened Python lower bounds — rich≥14.0.0, typer≥0.24.0, httpx≥0.28.1, pyyaml≥6.0.2

## Test plan

- [x] `prek run --all-files` passes
- [ ] Verify Fly.io deploy succeeds after merge (nginx minor bump + Alloy bump)
- [ ] Spot-check a workflow run with the new actions/checkout v6

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

Reviewed-on: #307

.forgejo/workflows/branch-cleanup.yaml

@@ -26,7 +26,7 @@ jobs:
     runs-on: k8s
     steps:
       - name: Checkout
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - name: Run branch cleanup
         env: