Initial commit: MusicDownload con UI pywebview

- Frontend HTML/CSS/JS in webui/ (stile Spotify-like, hero gradient, modal blur)
- API bridge JS<->Python in api/bridge.py
- Core invariato: downloader yt-dlp, upgrader, spotify client, config
- Build scripts macOS (WebKit) e Windows (EdgeChromium)
- .gitignore esclude credenziali (config.json, cookies.txt) e artefatti build

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

main.py

@@ -0,0 +1,42 @@
+"""MusicDownload — Entry point (pywebview + WebKit/EdgeChromium)."""
+
+import os
+import sys
+from pathlib import Path
+
+import webview
+
+from api.bridge import Api
+
+
+def _resource_path(*parts) -> str:
+    """Trova il path di una risorsa sia in dev che bundled (PyInstaller)."""
+    if getattr(sys, "frozen", False):
+        base = Path(sys._MEIPASS)  # type: ignore[attr-defined]
+    else:
+        base = Path(__file__).resolve().parent
+    return str(base.joinpath(*parts))
+
+
+def main():
+    api = Api()
+    index_path = _resource_path("webui", "index.html")
+
+    window = webview.create_window(
+        title="MusicDownload",
+        url=index_path,
+        js_api=api,
+        width=1080,
+        height=720,
+        min_size=(900, 600),
+        background_color="#0A0A0A",
+        resizable=True,
+    )
+    api.window = window
+
+    # Disable native menu / set dark on macOS
+    webview.start(debug=False)
+
+
+if __name__ == "__main__":
+    main()