feat: support multiple Gitea instances for actions runner

The gitea-actions role now uses a `gitea_runners` list instead of a
single `gitea_instance_url`. Each instance gets its own config, systemd
service, working directory, and cache. Migrates from the old single
`act_runner.service` to per-instance `act_runner-{name}.service`.

Adds git.skudak.com alongside git.debyl.io as runner targets.

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

ansible/roles/gitea-actions/defaults/main.yml

@@ -3,7 +3,16 @@ gitea_runner_user: gitea-runner
 gitea_runner_home: /home/gitea-runner
 gitea_runner_version: "0.2.13"
 gitea_runner_arch: linux-amd64
-gitea_instance_url: https://git.debyl.io
+
+# Multiple Gitea instances to run actions runners for
+gitea_runners:
+  - name: debyl
+    instance_url: https://git.debyl.io
+  - name: skudak
+    instance_url: https://git.skudak.com
+
+# Old single-instance format (replaced by gitea_runners list above):
+# gitea_instance_url: https://git.debyl.io
 
 # Paths
 act_runner_bin: /usr/local/bin/act_runner