Move CI to Gitea Actions

Single-runner workflow: test on every push; on v* tags cross-compile tefterd
for all platforms, build the Linux desktop app, and publish a Gitea release
via gitea.com/actions/release-action. Drop the GitHub workflow; document the
runner requirement and manual macOS/Windows desktop builds in the README.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -106,5 +106,22 @@ make server-all # linux/amd64, linux/arm64, darwin/arm64, windows/amd64
 make desktop    # Wails build (needs wails CLI + GTK/WebKit dev packages on Linux)
 ```
 
+## CI / Releases (Gitea Actions)
+
+`.gitea/workflows/ci.yml` runs tests on every push and, on a `v*` tag, builds
+`tefterd` for all four platforms plus the Linux desktop app and attaches them
+to a Gitea release. Requirements: Actions enabled on the repo and one Linux
+runner whose `ubuntu-latest` label maps to a Debian/Ubuntu-based image (the
+default `catthehacker/ubuntu:act-latest` works).
+
+```sh
+git tag v0.1.0 && git push origin v0.1.0   # cut a release
+```
+
+macOS/Windows desktop shells need a native machine: install Go + Node + the
+Wails CLI there and run `make desktop` (the result lands in
+`desktop/build/bin/`). The server binaries for those platforms come out of the
+Linux runner via cross-compilation.
+
 Repo layout: `frontend/` (Svelte + TS, all app logic incl. offline store + sync engine),
 `server/` (Go, stdlib HTTP + modernc.org/sqlite, no CGO), `desktop/` (Wails shell).