Add Windows support via a Tauri (WebView2) shell

zero-native has no Windows target yet, so add a parallel Tauri shell
for Windows that reuses the same frontend:

- src-tauri/: Rust commands (yt_search, yt_streams, store_load,
  store_save) mirroring the Zig bridge; spawns bundled yt-dlp.exe with
  CREATE_NO_WINDOW; data stored in app_data_dir
- frontend bridge now auto-detects window.__TAURI__ vs window.zero and
  routes accordingly; CSP updated for Tauri IPC
- tauri.conf.json bundles yt-dlp.exe as a resource and builds nsis/msi
- scripts/make-icon.js generates appicon.png for 'tauri icon'
- README: native Windows build steps + WSLg fallback note

README.md

@@ -24,21 +24,32 @@ or Node runtime.
 
 ## Architecture
 
+The **same frontend** drives two native shells:
+
+- **Linux / macOS** → zero-native (Zig + system WebView)
+- **Windows** → Tauri (Rust + WebView2) — see [Run on Windows](#run-on-windows-tauri)
+
 ```
-frontend/            Static web UI (no framework, no build step)
+frontend/            Static web UI (no framework, no build step) — shared
   index.html
   styles.css
-  app.js             Player engine + UI; calls window.zero.invoke(...)
-src/
+  app.js             Player engine + UI; auto-detects Tauri vs zero-native
+src/                 zero-native (Linux/macOS) shell
   main.zig           App definition + bridge handler registration
   bridge.zig         Native handlers: spawn yt-dlp, slim its JSON, local store
+src-tauri/           Tauri (Windows) shell
+  src/main.rs        Same handlers as Rust commands
+  tauri.conf.json    Window, CSP, bundle (icons, yt-dlp resource)
+  Cargo.toml
 scripts/
   setup-ytdlp.js     Downloads the standalone yt-dlp binary into ./bin
+  make-icon.js       Generates appicon.png for `tauri icon`
 bin/                 yt-dlp lands here (gitignored)
-app.zon              App manifest (window, engine, permissions, frontend dir)
+app.zon              zero-native manifest
 ```
 
-The web UI talks to the Zig side over the zero-native bridge:
+The web UI talks to the native side over whichever bridge is present
+(`window.__TAURI__.core.invoke` on Windows, `window.zero.invoke` elsewhere):
 
 | `window.zero.invoke(...)` | Native handler | Returns |
 |---|---|---|
@@ -58,8 +69,44 @@ and return only the compact fields the UI needs.
 - No system `yt-dlp` needed — the setup script bundles it. (On Linux/macOS the
   bundled build is self-contained; Python is not required.)
 
+## Run on Windows (Tauri)
+
+zero-native does **not** target Windows yet, so the Windows build uses a Tauri
+shell (Rust + the WebView2 runtime that ships with Windows 10/11). The result is
+a small standalone `.exe`/installer — no bundled Chromium or Node.
+
+**Build natively on the Windows machine** (cross-compiling a WebView2 app from
+WSL/Linux is unreliable, so do this on Windows):
+
+```powershell
+# Prerequisites (one time):
+#   • Rust          https://rustup.rs   (MSVC toolchain)
+#   • Microsoft C++ Build Tools (Desktop development with C++)
+#   • WebView2 runtime — preinstalled on Win11; on Win10 grab the Evergreen runtime
+#   • Node.js (to run the helper scripts + Tauri CLI)
+
+npm install                       # installs the Tauri CLI (@tauri-apps/cli)
+npm run setup                     # downloads yt-dlp.exe into .\bin
+npm run make-icon                 # writes appicon.png
+npm run tauri icon .\appicon.png  # expands it into src-tauri\icons\*
+
+npm run tauri:dev                 # hot dev window
+npm run tauri:build               # produces the installer (see below)
+```
+
+The installer lands in
+`src-tauri\target\release\bundle\` (`nsis\*-setup.exe` and `msi\*.msi`).
+`yt-dlp.exe` is bundled as an app resource, so the installed app is self-contained.
+
+> Already in WSL and just want it running fast? Your WSL is WSLg-enabled, so you
+> can instead build the **Linux** (zero-native) target and its window appears on
+> your Windows desktop — see [Setup & run](#setup--run). That needs WSL running
+> each time; the Tauri build above is a true standalone Windows app.
+
 ## Setup & run
 
+> Linux / macOS (zero-native). For Windows see [Run on Windows](#run-on-windows-tauri).
+
 ```bash
 # 1. Download the yt-dlp binary into ./bin
 npm run setup            # or: node scripts/setup-ytdlp.js