Remove act_runner from main docker-compose.yaml

The runner is CI/CD infrastructure, not part of the application.
Self-hosters cloning UMBRA don't need a runner. The runner now
lives as a standalone stack (documented in .claude/docs/).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yaml

@@ -63,31 +63,8 @@ services:
           memory: 128M
           cpus: "0.5"
 
-  act_runner:
-    image: gitea/act_runner:0.2.11
-    restart: unless-stopped
-    security_opt:
-      - label:disable
-    network_mode: host
-    volumes:
-      - act_runner_data:/data
-      - /var/run/docker.sock:/var/run/docker.sock
-      - ./act_runner_config.yaml:/etc/act_runner/config.yaml:ro
-    environment:
-      - CONFIG_FILE=/etc/act_runner/config.yaml
-      - GITEA_INSTANCE_URL=https://git.sentinelforest.xyz
-      - GITEA_RUNNER_REGISTRATION_TOKEN=${GITEA_RUNNER_REGISTRATION_TOKEN}
-      - GITEA_RUNNER_NAME=umbra-runner
-      - GITEA_RUNNER_LABELS=ubuntu-latest:docker://catthehacker/ubuntu:act-22.04
-    deploy:
-      resources:
-        limits:
-          memory: 256M
-          cpus: "1.0"
-
 volumes:
   postgres_data:
-  act_runner_data:
 
 networks:
   backend_net: