feat(workflows): wire TaskUnit/Orchestrator activities, add k8s deploy manifests

Implements real activity-calling logic in OrchestratorWorkflow and
TaskUnitWorkflow (previously stubs), adds GitDiffActivity, and expands
PlanningActivity's I/O to carry repo path and prior task results.

Adds k8s/ deployment manifests (worker Deployment, orchestrator Job,
Kustomize base) for the poimen-workflows Temporal worker, using a
dedicated Kubernetes namespace `poimen` and Temporal namespace
`poimen-harness` rather than sharing the Temporal server's own
`temporal`/`production` namespaces.

k8s/worker-deployment.yaml

@@ -0,0 +1,58 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: poimen-worker
+  namespace: poimen
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: poimen-worker
+  template:
+    metadata:
+      labels:
+        app: poimen-worker
+    spec:
+      containers:
+      - name: worker
+        image: golang:1.22-alpine
+        workingDir: /app
+        command: ["/bin/sh", "-c"]
+        args:
+          - |
+            apk add --no-cache git gcc musl-dev
+            git clone https://forgejo.riotpiao.com/rock/poimen.git /app
+            cd /app/workflows
+            go mod download
+            go run ./cmd/worker
+        env:
+        - name: TEMPORAL_NAMESPACE
+          valueFrom:
+            configMapKeyRef:
+              name: poimen-config
+              key: TEMPORAL_NAMESPACE
+        - name: TEMPORAL_HOSTPORT
+          valueFrom:
+            configMapKeyRef:
+              name: poimen-config
+              key: TEMPORAL_HOSTPORT
+        - name: ANTHROPIC_API_KEY
+          valueFrom:
+            secretKeyRef:
+              name: poimen-secrets
+              key: ANTHROPIC_API_KEY
+        resources:
+          requests:
+            memory: "512Mi"
+            cpu: "500m"
+          limits:
+            memory: "2Gi"
+            cpu: "2000m"
+        livenessProbe:
+          exec:
+            command:
+            - /bin/sh
+            - -c
+            - ps aux | grep -q "go run ./cmd/worker" && echo ok || exit 1
+          initialDelaySeconds: 30
+          periodSeconds: 10