Initial commit: dns-webhook MutatingAdmissionWebhook

Rewrites dnsPolicy+dnsConfig on ClusterFirst pods to distribute
queries across 3 randomly-selected auth-dns nameservers with
edns0/rotate/ndots:5. Includes Gitea CI workflow and README.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/main.yaml

@@ -0,0 +1,45 @@
+name: Build dns-webhook Image
+on:
+  push:
+    branches: [main]
+jobs:
+  build:
+    runs-on: fritzlab
+    steps:
+      - name: Check out repo
+        uses: actions/checkout@v4
+
+      - name: Log in to Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: code.fritzlab.net
+          username: ci-bot
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+
+      - name: Extract Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: code.fritzlab.net/dns/webhook
+          tags: |
+            type=raw,value=${{ github.run_number }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          provenance: false
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          network: host
+
+      - name: Clean up old image tags
+        run: |
+          tea login add --name ci --url https://code.fritzlab.net --token '${{ secrets.CI_BOT_TOKEN }}' --no-version-check
+          tea api '/packages/dns?type=container' | jq -r '.[] | select(.name=="webhook") | select(.version | test("^[0-9]+$")) | .version' \
+            | sort -n | head -n -3 \
+            | while read tag; do
+                echo "deleting webhook:$tag"
+                tea api -X DELETE "/packages/dns/container/webhook/$tag"
+              done