docs(workflows): clarify that GitHub only builds and serves while Gitea refreshes sources

Document the forge responsibilities across AGENTS.md, README.md, ARCHITECTURE.md, INGESTION.md, and the CI workflow headers: GitHub Actions only builds and serves (Pages deployment) without fetching data sources, while Gitea Actions exclusively runs the scheduled refresh and publishes the container image.

docs/ARCHITECTURE.md

@@ -224,7 +224,9 @@ that ordering is load-bearing.
 
 `Dockerfile` builds and serves this; the image runs typecheck and tests during build, ships no source
 or toolchain, and runs unprivileged. `.gitea/workflows/ci.yml` and `.gitlab-ci.yml` run the same
-gates and publish it, while `.github/workflows/ci.yml` builds and deploys to GitHub Pages.
+gates and publish it, while `.github/workflows/ci.yml` builds and deploys to GitHub Pages. GitHub
+only needs to build and serve, not refresh data sources; the scheduled refresh and container image
+publishing run exclusively on Gitea Actions.
 
 ### Hosting under a subpath