Rename act_runner to runner (#850)

## Consumer-facing breaking changes

- **Go module path**: `gitea.com/gitea/act_runner` → `gitea.com/gitea/runner`. Anything importing `act/...` or `internal/...` packages (notably Gitea itself) must update imports.
- **Binary name**: `act_runner` → `gitea-runner`. Wrapper scripts, systemd units, init scripts, and documentation referencing the binary by `act_runner` will break.
- **Docker image**: `gitea/act_runner` → `gitea/runner` (incl. `*-dind-rootless` variants). Users pulling `gitea/act_runner:nightly` etc. will get stale images. Note: the image name is `gitea/runner`, not `gitea/gitea-runner`.
- **Release artifact paths**: S3 directory `act_runner/{{.Version}}` → `gitea-runner/{{.Version}}`, and artifact filenames change with the new project name. Existing download URLs break.
- **Metrics namespace**: changed from `act_runner` to `gitea_runner` (e.g. `act_runner_jobs_total` → `gitea_runner_jobs_total`); existing monitors/dashboards must be updated.
- **ldflags version path**: `gitea.com/gitea/act_runner/internal/pkg/ver.version` → `gitea.com/gitea/runner/internal/pkg/ver.version`. Affects anyone building with custom ldflags.
- **Kubernetes example resource names**: `act-runner` / `act-runner-vol` → `runner` / `runner-vol`. Users who copied the manifests verbatim will see resource churn on apply.
- **s6 service name**: `scripts/s6/act_runner/` → `scripts/s6/gitea-runner/` (image-internal; only matters for downstream image overrides).

Unchanged: YAML config field names, env vars (`GITEA_*`), CLI flags/subcommands, registration file format.
---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/850
Reviewed-by: Zettat123 <39446+zettat123@noreply.gitea.com>
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Reviewed-by: Nicolas <bircni@icloud.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-committed-by: Lunny Xiao <xiaolunwen@gmail.com>

internal/pkg/config/config.example.yaml

@@ -1,9 +1,9 @@
 # Example configuration file, it's safe to copy this as the default config file without any modification.
 
 # You don't have to copy this file to your instance,
-# just run `./act_runner generate-config > config.yaml` to generate a config file.
+# just run `./gitea-runner generate-config > config.yaml` to generate a config file.
 
-# Logging for the act_runner process itself (messages printed to stderr).
+# Logging for the runner process itself (messages printed to stderr).
 # This does not control how workflow step output is streamed to the Gitea UI;
 # tune that with runner.log_report_* below.
 log:
@@ -83,19 +83,19 @@ cache:
   # 0 means to use a random available port.
   port: 0
   # The external cache server URL. Valid only when enable is true.
-  # If it's specified, act_runner will use this URL as the ACTIONS_CACHE_URL rather than start a server by itself.
+  # If it's specified, runner will use this URL as the ACTIONS_CACHE_URL rather than start a server by itself.
   # The URL should generally end with "/".
   # Requires external_secret below to be set to the same value on both this runner and the cache-server.
   external_server: ""
-  # Shared secret between this runner and the external `act_runner cache-server`. Required when external_server
-  # (or `act_runner cache-server`) is in use: the runner pre-registers each job's ACTIONS_RUNTIME_TOKEN with the
+  # Shared secret between this runner and the external `gitea-runner cache-server`. Required when external_server
+  # (or `gitea-runner cache-server`) is in use: the runner pre-registers each job's ACTIONS_RUNTIME_TOKEN with the
   # cache-server, and the cache-server enforces bearer auth + per-repo cache isolation.
   external_secret: ""
 
 container:
   # Specifies the network to which the container will connect.
   # Could be host, bridge or the name of a custom network.
-  # If it's empty, act_runner will create a network automatically.
+  # If it's empty, runner will create a network automatically.
   # Deprecated: `network_mode` is still accepted for old configs; use `network` instead.
   network: ""
   # Whether to use privileged mode or not when launching task containers (privileged mode is required for Docker-in-Docker).
@@ -103,7 +103,7 @@ container:
   # Any other options to be used when the container is started (e.g., --add-host=my.gitea.url:host-gateway).
   options:
   # The parent directory of a job's working directory.
-  # NOTE: There is no need to add the first '/' of the path as act_runner will add it automatically. 
+  # NOTE: There is no need to add the first '/' of the path as runner will add it automatically.
   # If the path starts with '/', the '/' will be trimmed.
   # For example, if the parent directory is /path/to/my/dir, workdir_parent should be path/to/my/dir
   # If it's empty, /workspace will be used.
@@ -119,17 +119,17 @@ container:
   #   - '**'
   valid_volumes: []
   # Overrides the docker client host with the specified one.
-  # If it's empty, act_runner will find an available docker host automatically.
-  # If it's "-", act_runner will find an available docker host automatically, but the docker host won't be mounted to the job containers and service containers.
+  # If it's empty, runner will find an available docker host automatically.
+  # If it's "-", runner will find an available docker host automatically, but the docker host won't be mounted to the job containers and service containers.
   # If it's not empty or "-", the specified docker host will be used. An error will be returned if it doesn't work.
   docker_host: ""
   # Pull docker image(s) even if already present
   force_pull: true
   # Rebuild docker image(s) even if already present
   force_rebuild: false
-  # Always require a reachable docker daemon, even if not required by act_runner
+  # Always require a reachable docker daemon, even if not required by runner
   require_docker: false
-  # Timeout to wait for the docker daemon to be reachable, if docker is required by require_docker or act_runner
+  # Timeout to wait for the docker daemon to be reachable, if docker is required by require_docker or runner
   docker_timeout: 0s
   # Bind the workspace to the host filesystem instead of using Docker volumes.
   # This is required for Docker-in-Docker (DinD) setups when jobs use docker compose