v5: standalone Tauri rewrite — Rust backend + TypeScript UI

Complete rewrite from the Python/Tkinter app to a native Tauri 2 desktop
app. Drops the song-detection feature, so it needs no Python and no ML
model — just ffmpeg. Replaces video_concat.py entirely.

- Rust backend (src-tauri): stream-copy concat via ffmpeg with honest
  real-time progress (-progress pipe:1, out_time vs total duration), held
  at 99% through the +faststart finalising pass so the bar never jumps
- ffprobe duration scanning parallelised across threads; cancel kills the
  whole ffmpeg process tree; CREATE_NO_WINDOW hides console flashes
- BiliBili Live filename helper ported to Rust (bililive_rename)
- TypeScript UI, no framework: tiny h() DOM helper, drag-and-drop,
  reorderable/checkable file list with live totals, light/dark theme,
  reusable toast + progress components
- Optional delete-originals-after-merge with a clear warning
- New app icon (three clips merging into one); build.bat assembles a
  portable folder with ffmpeg/ffprobe bundled next to the exe
- Ignore tauri-generated gen/schemas (regenerated on every build)

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

vite.config.ts

@@ -0,0 +1,30 @@
+import { defineConfig } from "vite";
+
+// @ts-expect-error process is a nodejs global
+const host = process.env.TAURI_DEV_HOST;
+
+// https://vite.dev/config/
+export default defineConfig(async () => ({
+
+  // Vite options tailored for Tauri development and only applied in `tauri dev` or `tauri build`
+  //
+  // 1. prevent Vite from obscuring rust errors
+  clearScreen: false,
+  // 2. tauri expects a fixed port, fail if that port is not available
+  server: {
+    port: 1420,
+    strictPort: true,
+    host: host || false,
+    hmr: host
+      ? {
+          protocol: "ws",
+          host,
+          port: 1421,
+        }
+      : undefined,
+    watch: {
+      // 3. tell Vite to ignore watching `src-tauri`
+      ignored: ["**/src-tauri/**"],
+    },
+  },
+}));