feat: add feature branch deployments with per-branch isolation

Enable deploying feature branches into isolated environments on the same
k3s cluster. Each branch gets its own namespace (cam-<slug>), PostgreSQL
schema, and OpenSearch index prefix for data isolation while sharing the
underlying infrastructure.

- Make OpenSearch index prefix and DB schema configurable via env vars
  (defaults preserve existing behavior)
- Restructure deploy/ into Kustomize base + overlays (main/feature)
- Extend CI to build Docker images for all branches, not just main
- Add deploy-feature job with namespace creation, secret copying,
  Traefik Ingress routing (<slug>-api/ui.cameleer.siegeln.net)
- Add cleanup-branch job to remove namespace, PG schema, OS indices
  on branch deletion
- Install required tools (git, jq, curl) in CI deploy containers

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/base/ui.yaml

@@ -0,0 +1,71 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: cameleer3-ui-config
+data:
+  config.js: |
+    window.__CAMELEER_CONFIG__ = {
+      apiBaseUrl: 'http://localhost:8081/api/v1',
+    };
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: cameleer3-ui
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: cameleer3-ui
+  template:
+    metadata:
+      labels:
+        app: cameleer3-ui
+    spec:
+      imagePullSecrets:
+        - name: gitea-registry
+      containers:
+        - name: ui
+          image: gitea.siegeln.net/cameleer/cameleer3-server-ui:latest
+          ports:
+            - containerPort: 80
+          env:
+            - name: CAMELEER_API_URL
+              value: "http://cameleer3-server:8081"
+          volumeMounts:
+            - name: config
+              mountPath: /usr/share/nginx/html/config.js
+              subPath: config.js
+          resources:
+            requests:
+              memory: "32Mi"
+              cpu: "10m"
+            limits:
+              memory: "64Mi"
+              cpu: "100m"
+          livenessProbe:
+            httpGet:
+              path: /healthz
+              port: 80
+            periodSeconds: 10
+          readinessProbe:
+            httpGet:
+              path: /healthz
+              port: 80
+            periodSeconds: 5
+      volumes:
+        - name: config
+          configMap:
+            name: cameleer3-ui-config
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: cameleer3-ui
+spec:
+  type: ClusterIP
+  selector:
+    app: cameleer3-ui
+  ports:
+    - port: 80
+      targetPort: 80