chore: add Kubernetes deployment manifests and Gitea Actions build workflow

Mirror the pr_reviewer deployment pattern: Gitea Actions builds a multi-arch
image in the gitea-runner namespace, pushes to git.aridgwayweb.com, recreates
the steward namespace with regcred + env secret, and applies kube manifests.
Add .omo/ to .gitignore.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

kube/steward_deployment.yaml

@@ -0,0 +1,55 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: steward-deployment
+  labels:
+    app: steward
+  namespace: steward
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: steward
+  template:
+    metadata:
+      labels:
+        app: steward
+    spec:
+      containers:
+      - name: steward
+        image: git.aridgwayweb.com/armistace/steward:latest
+        envFrom:
+        - secretRef:
+            name: steward-env
+        env:
+        - name: THREAD_MEMORY_PATH
+          value: /data/thread_memory.json
+        volumeMounts:
+        - name: steward-data
+          mountPath: /data
+        resources:
+          requests:
+            memory: "256Mi"
+            cpu: "100m"
+          limits:
+            memory: "1Gi"
+            cpu: "500m"
+      volumes:
+      - name: steward-data
+        persistentVolumeClaim:
+          claimName: steward-storage
+      imagePullSecrets:
+        - name: regcred
+---
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: steward-storage
+  namespace: steward
+spec:
+  accessModes:
+    - ReadWriteOnce
+  storageClassName: longhorn
+  resources:
+    requests:
+      storage: 1Gi

kube/steward_service.yaml

@@ -0,0 +1,14 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: steward-service
+  namespace: steward
+spec:
+  type: NodePort
+  selector:
+    app: steward
+  ports:
+    - name: matrix-appservice
+      port: 8000
+      targetPort: 8000
+      nodePort: 30002