Fix MTU for all Docker networks and add DinD readiness wait

- Add --default-network-opt to apply MTU=1340 to custom networks
  (not just default bridge) that act_runner creates per job
- Revert container.network to default (custom per-job network)
- Add DinD TLS cert readiness check before starting runner daemon

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gitea-runner/deployment.yaml

@@ -25,7 +25,7 @@ data:
         - "ubuntu-22.04:docker://catthehacker/ubuntu:act-22.04"
         - "self-hosted:host"
     container:
-      network: "bridge"
+      network: ""
       privileged: false
       options:
       valid_volumes: []
@@ -58,6 +58,11 @@ spec:
             - sh
             - -c
             - |
+              # Wait for DinD TLS certs to be ready
+              echo "Waiting for Docker daemon..."
+              while [ ! -f /certs/client/ca.pem ]; do sleep 1; done
+              sleep 2
+              echo "Docker daemon is ready"
               # Register if not already registered
               if [ ! -f /data/.runner ]; then
                 act_runner register --no-interactive \
@@ -87,6 +92,7 @@ spec:
           image: docker:dind
           args:
             - --mtu=1340
+            - --default-network-opt=bridge=com.docker.network.driver.mtu=1340
           securityContext:
             privileged: true
           env: