Add Gitea Actions image-build workflow

Distilled from the house pattern across sibling projects: tag push +
workflow_dispatch triggers, REGISTRY_TOKEN login, raw docker build/push
to gitea.home.hrajfrisbee.cz. Adds a lightweight test gate, an immutable
sha-<12> tag, :latest only on real tag pushes, and a concurrency group.

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

CLAUDE.md

@@ -199,8 +199,18 @@ Always append a `Co-Authored-By` trailer to indicate AI assistance:
 
     Co-Authored-By: Claude <noreply@anthropic.com>
 
-TODO: no `.gitea/workflows/` CI pipeline exists yet — add a CI/CD subsection here once
-one is set up.
+### CI/CD
+
+`.gitea/workflows/build.yaml` builds the manager image and pushes it to the Gitea
+registry. Triggers: any tag push, or manual `workflow_dispatch` with a `tag` input.
+A lightweight `check` job (`go vet` / `go build` / `go test -short`) gates the build.
+
+- Images: `gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator:<tag>` plus an
+  immutable `sha-<12-char-commit>` tag on every build; `:latest` moves only on real
+  tag pushes, never on manual dispatch.
+- Requires the `REGISTRY_TOKEN` repo secret (Gitea PAT with `write:package`),
+  same convention as the other projects on this Gitea instance.
+- The commit is baked into the binary via the `GIT_COMMIT` build arg (see Dockerfile).
 
 ## Gotchas