Switch to master branch + Gitea Actions

- Move CI/release workflows from .github/workflows to .gitea/workflows (Gitea Actions),
  targeting the master branch.
- docker-publish: push to the Gitea container registry (git.finalfactory.de) with a
  lowercased image name; login via github.token or a PACKAGES_TOKEN secret.
- version-tag: gitea-actions bot identity; optional RELEASE_TOKEN to re-trigger the image build.
- Update README/CLAUDE.md/Unraid template/build-and-push.ps1 to the Gitea registry + master.

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

README.md

@@ -74,8 +74,10 @@ Architecture, project layout and conventions live in [`CLAUDE.md`](CLAUDE.md).
 
 ## Releasing
 
-Edit the [`VERSION`](VERSION) file on `main`; CI tags `vX.Y.Z` and builds/pushes a multi-arch image
-(`.github/workflows/`). Locally: `pwsh deploy/build-and-push.ps1 -Push`.
+Edit the [`VERSION`](VERSION) file on `master`; Gitea Actions tags `vX.Y.Z` and builds/pushes a
+multi-arch image to the Gitea container registry (`.gitea/workflows/`). Locally:
+`pwsh deploy/build-and-push.ps1 -Registry git.finalfactory.de -Image finalfactory/metervault -Push`.
+Requires a Docker-capable `act_runner`; the image build itself is self-contained.
 
 ## License