Release 0.1.0: MIT license, changelog, multi-arch Docker image without CLI builds

- LICENSE (MIT), CHANGELOG for 0.1.0, README overhaul
- docker-compose.release.yml pulling the registry image
- Dockerfile cross-compiles the server with cargo-zigbuild for amd64 and arm64;
  the terminal client is no longer built into the image
- Server, install script and settings point to a source install of the
  terminal client when no prebuilt binaries are available (/info: cli_builds)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/api.rs

@@ -180,6 +180,13 @@ fn cli_dir() -> PathBuf {
     std::env::var("CODECRAFT_CLI_DIR").map(PathBuf::from).unwrap_or_else(|_| PathBuf::from("/app/cli"))
 }
 
+/// Whether this server ships prebuilt terminal client binaries (the release image does not).
+pub(crate) fn cli_builds_available() -> bool {
+    std::fs::read_dir(cli_dir()).map(|mut d| d.any(|e| e.is_ok_and(|e| e.file_name().to_string_lossy().starts_with("codecraft-")))).unwrap_or(false)
+}
+
+const CLI_SOURCE_HINT: &str = "build it from source: cargo install --locked --git https://git.familie-zink.org/zink/codecraft codecraft-cli";
+
 /// The server's public base URL (config, else from the request).
 fn public_base(app: &App, headers: &axum::http::HeaderMap) -> String {
     let cfg = app.config();
@@ -213,7 +220,7 @@ async fn cli_download(Path(target): Path<String>) -> Response {
             bytes,
         )
             .into_response(),
-        Err(_) => (StatusCode::NOT_FOUND, format!("no codecraft build for {target} on this server")).into_response(),
+        Err(_) => (StatusCode::NOT_FOUND, format!("no prebuilt codecraft for {target} on this server – {CLI_SOURCE_HINT}\n")).into_response(),
     }
 }