fix(desktop): use kebab-case productName for bundle naming

tauri-action expects kebab-case artifact names but Tauri 2 uses
productName exactly as specified. Use 'spirit-stream' for bundles
while keeping 'SpiritStream' as the window title.

Author: radicalkjax

apps/desktop/src-tauri/tauri.conf.json

@@ -1,6 +1,6 @@
 {
   "$schema": "../../../node_modules/@tauri-apps/cli/config.schema.json",
-  "productName": "SpiritStream",
+  "productName": "spirit-stream",
   "version": "1.1.1",
   "identifier": "com.spiritstream.desktop",
   "build": {