Enable zot registry auth + wire CI credentials (#237)

## Summary

- Enable OIDC + API key authentication on zot registry with three-tier accessControl
  - `anonymousPolicy: ["read"]` — anyone can pull
  - `artifact-workloads` group: `["read", "create"]` — CI push, no overwrite/delete
  - `admins` group: `["read", "create", "update", "delete"]` — break-glass
- Wire both CI push paths (Dagger and Nix/skopeo) with `ZOT_CI_API_KEY` credentials
- Add `artifact-workloads` PolicyBinding in Authentik blueprint for zot app access
- Add `ZOT_CI_API_KEY` to Forgejo Actions secrets via existing ansible role

Completes the `wire-ci-registry-auth` and `harden-zot-registry` Mikado cards.

## Manual Deployment Steps (after merge)

1. Deploy Authentik blueprint: `argocd app sync authentik`
2. In Authentik admin UI: set a password for the `zot-ci` service account
3. Deploy zot config: `mise run provision-indri -- --tags zot`
4. Log in to `https://registry.ops.eblu.me` as `zot-ci` via OIDC → generate API key
5. Store API key in 1Password as `zot-ci-apikey` in blumeops vault
6. Sync Forgejo secrets: `mise run provision-indri -- --tags forgejo_actions_secrets`
7. Trigger a test container build to verify CI push
8. Verify anonymous pull: `curl -sf https://registry.ops.eblu.me/v2/_catalog`

## Uncertainties

- **Zot `accessControl` group matching with OIDC:** Groups from Authentik's `profile` scope claim should map to zot policy groups, but the exact claim-to-group matching needs runtime verification
- **`http.auth.apikey: true`:** This config key is documented but needs verification against the specific zot version built from source on indri
- **API key permissions:** Need to confirm zot API keys inherit the generating user's group for accessControl evaluation

## Test Plan

- [ ] `mise run provision-indri -- --check --diff --tags zot` shows expected config changes
- [ ] Anonymous pull works after deploy
- [ ] Unauthenticated push fails (401)
- [ ] OIDC browser login redirects to Authentik and back
- [ ] API key push works after key generation
- [ ] CI push succeeds with both Dagger and skopeo paths
- [ ] `mise run services-check` passes

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

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/237

.forgejo/workflows/build-container-nix.yaml

@@ -129,6 +129,8 @@ jobs:
 
       - name: Push to registry
         if: steps.check.outputs.exists == 'true'
+        env:
+          ZOT_CI_API_KEY: ${{ secrets.ZOT_CI_API_KEY }}
         run: |
           CONTAINER="${{ matrix.container }}"
           VERSION="${{ steps.meta.outputs.version }}"
@@ -137,6 +139,7 @@ jobs:
 
           echo "Pushing to $IMAGE"
           skopeo copy \
+            --dest-creds="zot-ci:$ZOT_CI_API_KEY" \
             "docker-archive:result" \
             "docker://$IMAGE"
           echo "Push complete: $IMAGE"

.forgejo/workflows/build-container.yaml

@@ -97,9 +97,12 @@ jobs:
 
       - name: Publish
         if: steps.check.outputs.exists == 'true'
+        env:
+          ZOT_CI_API_KEY: ${{ secrets.ZOT_CI_API_KEY }}
         run: |
           dagger call publish \
             --src=. \
             --container-name=${{ matrix.container }} \
             --version=${{ steps.meta.outputs.version }} \
-            --commit-sha=${{ steps.meta.outputs.sha }}
+            --commit-sha=${{ steps.meta.outputs.sha }} \
+            --registry-password=env:ZOT_CI_API_KEY