Revert "fix(gitea): revert cache workarounds, rely on CONFIG_FILE fix instead"

This reverts commit b62b9b1871.

gitea/runner-config.yaml

@@ -17,12 +17,26 @@ cache:
   dir: ""
   host: ""
   port: 0
-  external_server: ""
+  # Both the shared network approaches we tried (a custom network name, then
+  # Docker's real "bridge" network) failed to make job containers reachable
+  # from/to this daemon's own embedded cache server - its host/port config
+  # is also unreliable in this act_runner version (confirmed by others: a
+  # fixed port still gets silently ignored in favor of a random one, see
+  # https://codeberg.org/forgejo/docs/issues/996). Using a dedicated
+  # `cache-server` process instead (see runner-cache-server in compose.yml),
+  # whose --host/--port CLI flags are documented and confirmed to actually
+  # work, reached via host.docker.internal + a published fixed port (proven
+  # reachable end-to-end from an isolated per-task-style container).
+  external_server: "http://host.docker.internal:8088/"
+  external_secret_file: "/data/cache_secret"
 
 container:
   network: ""
   privileged: false
-  options: "-v /var/run/docker.sock:/var/run/docker.sock"
+  # --add-host is what makes host.docker.internal (used for
+  # cache.external_server above) resolve inside job containers on Linux -
+  # Docker only wires it up automatically on Docker Desktop (Mac/Windows).
+  options: "-v /var/run/docker.sock:/var/run/docker.sock --add-host=host.docker.internal:host-gateway"
   workdir_parent: ""
   valid_volumes: []
   docker_host: ""