Custom workspace dropdown + Launch-Unreal button

Replace the ugly native <select> on the connect screen with a themed
custom dropdown (Select component). Add a Launch-Unreal button that appears
when the chosen working folder contains a .uproject: backend find_uproject
resolves the scope to disk and searches it (and one level down); the button
opens the project via the opener plugin. Bundled the UE icon (currentColor,
so white-on-dark / black-on-light per theme). New strings translated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/capabilities/default.json

@@ -6,6 +6,7 @@
   "permissions": [
     "core:default",
     "opener:default",
+    "opener:allow-open-path",
     "core:window:allow-start-dragging",
     "core:window:allow-minimize",
     "core:window:allow-toggle-maximize",