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/clusterrolebinding_gateway-cert-operator.yaml

@@ -0,0 +1,15 @@
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  name: gateway-cert-operator
+  labels:
+    app.kubernetes.io/name: gateway-cert-operator
+    app.kubernetes.io/component: operator
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: gateway-cert-operator
+subjects:
+  - kind: ServiceAccount
+    name: gateway-cert-operator
+    namespace: gateway-cert-operator-system