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/p4.ts

@@ -72,6 +72,7 @@ export const p4 = {
   describe: (change: string) => invoke<Describe>("p4_describe", { change }),
   undoChange: (change: string) => invoke<string>("p4_undo_change", { change }),
   openInExplorer: (target: string) => invoke<void>("open_in_explorer", { target }),
+  findUproject: (scope: string) => invoke<string>("find_uproject", { scope }),
   readDepot: async (depot: string): Promise<ArrayBuffer> => {
     const r: unknown = await invoke("read_depot", { depot });
     if (r instanceof ArrayBuffer) return r;