Build custom Kingfisher container from sporked deploy branch (#318)

## Summary

- Add Dockerfile for Kingfisher built from source (sporked deploy branch)
- Multi-stage: Rust build with Boost/vectorscan, debian-slim runtime
- Switch CronJob from upstream `ghcr.io/mongodb/kingfisher` to `registry.ops.eblu.me/blumeops/kingfisher`
- Add kingfisher to service-versions.yaml (version tracks upstream main SHA)
- Document spork workflow in CLAUDE.md

## Test plan

- [ ] Build container: `mise run container-build-and-release kingfisher 1d37d29`
- [ ] Verify image on registry: `mise run container-list`
- [ ] Update kustomization newTag
- [ ] Sync ArgoCD kingfisher app from branch
- [ ] Trigger manual CronJob and verify scan completes
- [ ] Verify reports on sifaka

Reviewed-on: #318

service-versions.yaml

@@ -285,6 +285,13 @@ services:
     upstream-source: https://github.com/prowler-cloud/prowler/releases
     notes: CIS Kubernetes Benchmark scanner; weekly CronJob on minikube-indri
 
+  - name: kingfisher
+    type: argocd
+    last-reviewed: 2026-03-29
+    current-version: "165768b"
+    upstream-source: https://github.com/mongodb/kingfisher/releases
+    notes: Secret scanner; sporked from upstream with --clone-url-base patch. Version is upstream main SHA.
+
   - name: forgejo
     type: ansible
     last-reviewed: 2026-03-28