ci(deploy): extract reload-caddy composite action

First composite action in the repo (establishes the convention). Lifts the
Caddy reload step verbatim from nightly.yml/release.yml — DooD privileged
sibling + nsenter to systemctl reload caddy, pinned alpine digest, reload
not restart. No inputs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/actions/reload-caddy/action.yml

@@ -0,0 +1,41 @@
+name: Reload Caddy
+description: >-
+  Reload the host Caddy service from a DooD job container via a privileged
+  sibling container and nsenter. No inputs.
+
+runs:
+  using: composite
+  steps:
+    - name: Reload Caddy
+      shell: bash
+      # Apply any committed Caddyfile changes before smoke-testing the
+      # public surface. Without this step, a Caddyfile edit lands in the
+      # repo but Caddy keeps serving the previous config until someone
+      # reloads it manually — the smoke test would then catch a stale
+      # header or a still-proxied /actuator route rather than confirming
+      # the current config is live.
+      #
+      # The runner executes job steps inside Docker containers (DooD).
+      # `systemctl` is not present in container images and cannot reach
+      # the host's systemd directly. We use the Docker socket (mounted
+      # into every job container via runner-config.yaml) to spin up a
+      # privileged sibling container in the host PID namespace; nsenter
+      # then enters the host's namespaces so systemctl talks to the real
+      # host systemd daemon. No sudoers entry is required — the Docker
+      # socket already grants root-equivalent host access.
+      #
+      # Alpine is used: ~5 MB vs ~70 MB for ubuntu, no unnecessary
+      # tooling, and the digest is pinned so any upstream change requires
+      # an explicit bump PR. util-linux (which ships nsenter) is installed
+      # at run time; apk add takes ~1 s on the warm VPS cache.
+      #
+      # `reload` not `restart`: reload sends SIGHUP so Caddy re-reads its
+      # config in-process without dropping TLS connections. `restart`
+      # would briefly stop the service, losing in-flight requests.
+      #
+      # If Caddy is not running this step fails fast before the smoke test
+      # issues a misleading "port 443 refused" error.
+      run: |
+        docker run --rm --privileged --pid=host \
+          alpine:3.21@sha256:48b0309ca019d89d40f670aa1bc06e426dc0931948452e8491e3d65087abc07d \
+          sh -c 'apk add --no-cache util-linux -q && nsenter -t 1 -m -u -n -p -i -- /bin/systemctl reload caddy'