chore(infra): act_runner capacity 4 + disable cache server

Add an act_runner config.yaml (ConfigMap, CONFIG_FILE env): capacity 4 so the
typecheck matrix + image builds run in parallel instead of one-at-a-time, and
cache.enabled: false (we removed the setup-node cache; the cache server isn't
reachable from the DinD job containers anyway).

infrastructure/production/fleet/ci/gitea-runner.yaml

@@ -27,6 +27,28 @@ spec:
     requests:
       storage: 2Gi
 ---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: act-runner-config
+  namespace: gitea-runner
+data:
+  config.yaml: |
+    log:
+      level: info
+    runner:
+      # Run several jobs at once (the 4-app typecheck matrix + image builds)
+      # instead of one-at-a-time. The AX41 has headroom.
+      capacity: 4
+      timeout: 3h
+      labels:
+        - "ubuntu-latest:docker://catthehacker/ubuntu:act-22.04"
+        - "docker:docker://docker:27-cli"
+    cache:
+      # We don't use the Actions cache (setup-node cache was removed); disabling
+      # avoids the cache server the DinD job containers can't reach anyway.
+      enabled: false
+---
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -69,11 +91,15 @@ spec:
               value: /certs/client
             - name: DOCKER_TLS_VERIFY
               value: "1"
+            - name: CONFIG_FILE
+              value: /config/config.yaml
           volumeMounts:
             - name: runner-data
               mountPath: /data
             - name: docker-certs
               mountPath: /certs
+            - name: runner-config
+              mountPath: /config
         - name: dind
           image: docker:27-dind
           securityContext:
@@ -94,3 +120,6 @@ spec:
           emptyDir: {}
         - name: dind-storage
           emptyDir: {}
+        - name: runner-config
+          configMap:
+            name: act-runner-config