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>

examples/vm/rootless-docker.md

@@ -1,12 +1,12 @@
-## Using Rootless Docker with`act_runner`
+## Using Rootless Docker with`gitea-runner`
 
-Here is a simple example of how to set up `act_runner` with rootless Docker. It has been created with Debian, but other Linux should work the same way.
+Here is a simple example of how to set up `gitea-runner` with rootless Docker. It has been created with Debian, but other Linux should work the same way.
 
 Note: This procedure needs a real login shell -- using `sudo su` or other method of accessing the account will fail some of the steps below.
 
 As `root`:
 
-- Create a user to run both `docker` and `act_runner`. In this example, we use a non-privileged account called `rootless`.
+- Create a user to run both `docker` and `gitea-runner`. In this example, we use a non-privileged account called `rootless`.
 
 ```bash
  useradd -m rootless
@@ -38,36 +38,36 @@ export DOCKER_HOST=unix:///run/user/$(id -u)/docker.sock
 ```
 
 - Reboot. Ensure that the Docker process is working.
-- Create a directory for saving `act_runner` data between restarts
+- Create a directory for saving `gitea-runner` data between restarts
 
- `mkdir /home/rootless/act_runner`
+ `mkdir /home/rootless/gitea-runner`
 
 - Register the runner from the data directory
 
 ```bash
- cd /home/rootless/act_runner
- act_runner register
+ cd /home/rootless/gitea-runner
+ gitea-runner register
 ```
 
-- Generate a `act_runner` configuration file in the data directory. Edit the file to adjust for the system.
+- Generate a `gitea-runner` configuration file in the data directory. Edit the file to adjust for the system.
 
 ```bash
- act_runner generate-config >/home/rootless/act_runner/config
+ gitea-runner generate-config >/home/rootless/gitea-runner/config
 ```
 
-- Create a new user-level`systemd` unit file as `/home/rootless/.config/systemd/user/act_runner.service` with the following contents:
+- Create a new user-level`systemd` unit file as `/home/rootless/.config/systemd/user/gitea-runner.service` with the following contents:
 
 ```bash
  Description=Gitea Actions runner
- Documentation=https://gitea.com/gitea/act_runner
+ Documentation=https://gitea.com/gitea/runner
  After=docker.service
 
  [Service]
  Environment=PATH=/home/rootless/bin:/sbin:/usr/sbin:/home/rootless/bin:/home/rootless/bin:/home/rootless/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
  Environment=DOCKER_HOST=unix:///run/user/1001/docker.sock
- ExecStart=/usr/bin/act_runner daemon -c /home/rootless/act_runner/config
+ ExecStart=/usr/bin/gitea-runner daemon -c /home/rootless/gitea-runner/config
  ExecReload=/bin/kill -s HUP $MAINPID
- WorkingDirectory=/home/rootless/act_runner
+ WorkingDirectory=/home/rootless/gitea-runner
  TimeoutSec=0
  RestartSec=2
  Restart=always
@@ -88,8 +88,8 @@ export DOCKER_HOST=unix:///run/user/$(id -u)/docker.sock
 
 - Reboot
 
-After the system restarts, check that the`act_runner` is working and that the runner is connected to Gitea.
+After the system restarts, check that the`gitea-runner` is working and that the runner is connected to Gitea.
 
 ````bash
- systemctl --user status act_runner
- journalctl --user -xeu act_runner
+ systemctl --user status gitea-runner
+ journalctl --user -xeu gitea-runner