Add Gitea release workflow; pull image from registry by default

CI builds and pushes the comfyui-nvidia image to the Gitea container
registry on every v* tag, mirroring the figment release workflow. Compose
now references the registry image (with build context kept for local
iteration) and the docs reflect the pull-by-default flow.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -22,9 +22,14 @@ setup.
 ```sh
 cp .env.example .env
 # edit .env — set OPEN_WEBUI_SECRET_KEY at minimum
-docker compose up -d --build
+docker compose up -d
 ```
 
+`compose up` pulls the prebuilt ComfyUI image from
+`git.anomalous.dev/alphacentri/comfyui-nvidia` (CI publishes it on every
+`v*` tag — see [.gitea/workflows/release.yml](.gitea/workflows/release.yml)).
+Use `docker compose build` to rebuild locally when iterating on the Dockerfile.
+
 Then drop a checkpoint into the `comfyui-models` volume and finish the Open
 WebUI ComfyUI configuration. Full walkthrough in [SETUP.md](SETUP.md).