feat: add Gitea CI workflows and split deploy manifests

Add build and kubernetes-deploy Gitea Actions workflows, and split deploy/manifests.yaml into individual manifest files.

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

deploy/service_gateway-cert-operator-metrics.yaml

@@ -0,0 +1,16 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: gateway-cert-operator-metrics
+  namespace: gateway-cert-operator-system
+  labels:
+    app.kubernetes.io/name: gateway-cert-operator
+    app.kubernetes.io/component: metrics
+spec:
+  selector:
+    app.kubernetes.io/name: gateway-cert-operator
+  ports:
+    - name: metrics
+      port: 8080
+      targetPort: metrics
+      protocol: TCP