gitea: add actions runner and CI/CD deploy workflow

This will avoid me having to run "deploy" myself on my laptop.
All I will need to do is push a commit and it will self-deploy.

tests/gitea-runner.nix

@@ -0,0 +1,60 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+pkgs.testers.runNixOSTest {
+  name = "gitea-runner";
+  nodes.machine =
+    { pkgs, ... }:
+    {
+      services.gitea = {
+        enable = true;
+        database.type = "sqlite3";
+        settings = {
+          server = {
+            HTTP_PORT = 3000;
+            ROOT_URL = "http://localhost:3000";
+            DOMAIN = "localhost";
+          };
+          actions.ENABLED = true;
+          service.DISABLE_REGISTRATION = true;
+        };
+      };
+
+      specialisation.runner = {
+        inheritParentConfig = true;
+        configuration.services.gitea-actions-runner.instances.test = {
+          enable = true;
+          name = "ci";
+          url = "http://localhost:3000";
+          labels = [ "native:host" ];
+          tokenFile = "/var/lib/gitea/runner_token";
+        };
+      };
+    };
+
+  testScript = ''
+    start_all()
+
+    machine.wait_for_unit("gitea.service")
+    machine.wait_for_open_port(3000)
+
+    # Generate runner token
+    machine.succeed(
+        "su -l gitea -s /bin/sh -c '${pkgs.gitea}/bin/gitea actions generate-runner-token --work-path /var/lib/gitea' | tail -1 | sed 's/^/TOKEN=/' > /var/lib/gitea/runner_token"
+    )
+
+    # Switch to runner specialisation
+    machine.succeed(
+        "/run/current-system/specialisation/runner/bin/switch-to-configuration test"
+    )
+
+    # Start the runner (specialisation switch doesn't auto-start new services)
+    machine.succeed("systemctl start gitea-runner-test.service")
+    machine.wait_for_unit("gitea-runner-test.service")
+    machine.succeed("sleep 5")
+    machine.succeed("test -f /var/lib/gitea-runner/test/.runner")
+  '';
+}