feat: add act_runner service for Gitea Actions

Runs alongside Gitea, mounts Docker socket for Docker-based workflows.
Token passed via GITEA_RUNNER_TOKEN env var (set in gitea/.env on server).

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

gitea/docker-compose.yml

@@ -13,3 +13,17 @@ services:
     environment:
       - GITEA__database__DB_TYPE=sqlite3
       - GITEA__service__DISABLE_REGISTRATION=true
+
+  act_runner:
+    image: gitea/act_runner:latest
+    container_name: act_runner
+    restart: always
+    depends_on:
+      - gitea
+    volumes:
+      - /data/server-infra/act_runner:/data
+      - /var/run/docker.sock:/var/run/docker.sock
+    environment:
+      - GITEA_INSTANCE_URL=https://git.padelnomics.io
+      - GITEA_RUNNER_REGISTRATION_TOKEN=${GITEA_RUNNER_TOKEN}
+      - GITEA_RUNNER_NAME=hetzner