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/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    tauri_build::build()
+}