feat: migrate realtime-collab from Docker Compose to k3s

Add k3s manifests for postgres, redis, and backend

Fix users table constraint and init.sql

k3s/backend.yaml

@@ -0,0 +1,49 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: realtime-collab-backend
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: realtime-collab-backend
+  template:
+    metadata:
+      labels:
+        app: realtime-collab-backend
+    spec:
+      containers:
+        - name: backend
+          image: realtime-collab-backend:latest
+          imagePullPolicy: Never
+          ports:
+            - containerPort: 8080
+          envFrom:
+            - secretRef:
+                name: realtime-collab-secret
+          resources:
+            requests:
+              memory: "32Mi"
+              cpu: "50m"
+            limits:
+              memory: "128Mi"
+              cpu: "300m"
+          readinessProbe:
+            httpGet:
+              path: /health
+              port: 8080
+            initialDelaySeconds: 10
+            periodSeconds: 10
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: realtime-collab-backend-svc
+spec:
+  type: NodePort
+  selector:
+    app: realtime-collab-backend
+  ports:
+    - port: 8080
+      targetPort: 8080
+      nodePort: 30080