Add README, plugin citations, and multi-platform release CI.

Ship screenshots and third-party notices for the desktop shell, and
package Windows, macOS, deb, rpm, and Flatpak from GitHub Releases.

Co-authored-by: Cursor <cursoragent@cursor.com>

src-tauri/src/main.rs

@@ -0,0 +1,5 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+fn main() {
+    dsh_desktop_lib::run();
+}