Add release pipeline: AUR packaging, Gitea workflow, MIT license

Mirrors the gpupaper release convention: v* tags build x86_64/aarch64
tarballs (binary + leptos site + systemd unit), upload them as Gitea
release assets, push bendik/cnats to Docker Hub, and update the AUR
package with checksums from the release assets.

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

README.md

@@ -17,6 +17,17 @@ signed-in session (sender identity comes from the session, never the client)
 and fans messages out to browsers over Server-Sent Events. Any other NATS
 client on the bus can publish/subscribe to `chat.room.*` and participate.
 
+## Install
+
+- **Arch (AUR):** `yay -S cnats` — installs the binary, `cnats.service`, and
+  config at `/etc/cnats/env`; then `systemctl enable --now cnats`.
+- **Docker:** `docker run --env-file .env -p 3000:3000 bendik/cnats` (or the
+  compose file below).
+
+Releases are cut by the Gitea workflow in `.gitea/workflows/release.yml`: a
+`v*` tag builds x86_64 + aarch64 tarballs, publishes them as release assets,
+pushes the image to Docker Hub, and updates the AUR package.
+
 ## Prerequisites
 
 - Rust (stable) with the `wasm32-unknown-unknown` target