docs(gitea): swap runner base image to catthehacker/ubuntu:act-latest

node:20-bookworm has no docker CLI, which caused release-image.yml and
any workflow using docker login/buildx to fail with "docker: command
not found" despite the socket mount being in place.

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

.gitea/gitea_compose_qnap_all_in_one.md

@@ -86,9 +86,12 @@ services:
       - gitea
     environment:
       - GITEA_INSTANCE_URL=http://gitea:3000
-      - GITEA_RUNNER_REGISTRATION_TOKEN=${GITEA_RUNNER_REGISTRATION_TOKEN}
+      - GITEA_RUNNER_REGISTRATION_TOKEN=218iFl8s3a6uJxntyoobzu24pQJBGGVIWmdtJbXh
       - GITEA_RUNNER_NAME=qnap-runner-1
-      - GITEA_RUNNER_LABELS=ubuntu-latest:docker://node:20-bookworm,ubuntu-22.04:docker://node:20-bookworm
+      # catthehacker/ubuntu:act-latest statt node:20-bookworm, weil sonst
+      # `docker`-CLI in Job-Containern fehlt und Workflows wie release-image.yml
+      # (docker login/buildx) mit "docker: command not found" scheitern.
+      - GITEA_RUNNER_LABELS=ubuntu-latest:docker://catthehacker/ubuntu:act-latest,ubuntu-22.04:docker://catthehacker/ubuntu:act-22.04
       - CONFIG_FILE=/config.yaml
     networks:
       - gitea
@@ -223,6 +226,7 @@ Zusätzlich: QNAP **Storage & Snapshots** → Volume-Snapshots für `/share/Cont
 
 - Socket-Mount prüfen
 - `container.network` in der inline-generierten Runner-Config muss zum echten Docker-Netzwerknamen passen (`docker network ls`)
+- Fehler `docker: command not found` → Job-Container hat kein Docker-CLI. Runner-Label muss ein Image verwenden, das `docker` mitbringt (z.B. `catthehacker/ubuntu:act-latest`). `node:*`-Images reichen nicht, weil dort nur Node installiert ist
 
 **`uses: actions/checkout@v4` schlägt fehl:**