Video tab: modalita 'Solo audio' (estrazione MP3)

Aggiunto toggle Video/Solo audio nella tab Video. In modalita audio
yt-dlp scarica solo bestaudio ed estrae in MP3 al bitrate impostato
in Impostazioni (default 320 kbps), con embed thumbnail come la tab
Scarica.

- core/downloader.py: download_video() accetta audio_only e
  audio_bitrate; quando True usa format 'bestaudio/best' e
  --extract-audio --audio-format mp3
- api/bridge.py: start_video_download passa audio_only nel worker;
  log mostra 'Solo audio MP3 320K' vs 'Video 1080p'
- webui: segmented control 'Video (MP4)' / 'Solo audio (MP3)' rosa,
  selettore qualita nascosto in modalita audio, hint aggiornato

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

webui/css/style.css

@@ -615,6 +615,36 @@ input[type="number"]::-webkit-inner-spin-button {
 .log .l-warn { color: #FDCB6E; }
 .log .l-muted { color: var(--text-3); }
 
+/* ===============================
+   SEGMENTED CONTROL
+   =============================== */
+.segmented {
+  display: inline-flex;
+  background: var(--bg-input);
+  padding: 4px;
+  border-radius: var(--r-pill);
+  gap: 2px;
+}
+
+.seg-btn {
+  border: none;
+  background: transparent;
+  color: var(--text-2);
+  padding: 8px 18px;
+  border-radius: var(--r-pill);
+  cursor: pointer;
+  font-weight: 700;
+  font-size: 13px;
+  transition: background-color 0.15s, color 0.15s;
+}
+
+.seg-btn:hover:not(.active) { color: var(--text); }
+
+.seg-btn.active {
+  background: var(--pink);
+  color: #fff;
+}
+
 /* ===============================
    HINT BOX
    =============================== */

webui/index.html

@@ -144,6 +144,14 @@
           </div>
 
           <div class="field inline">
+            <label class="field-label">Modalità</label>
+            <div class="segmented" id="videoMode">
+              <button type="button" class="seg-btn active" data-mode="video">🎬 Video (MP4)</button>
+              <button type="button" class="seg-btn" data-mode="audio">🎵 Solo audio (MP3)</button>
+            </div>
+          </div>
+
+          <div class="field inline" id="videoQualityField">
             <label class="field-label">Qualità</label>
             <select id="videoQuality" class="input pill input-sm">
               <option value="best">Migliore disponibile</option>
@@ -155,7 +163,10 @@
 
           <div class="hint">
             <span class="hint-ico">ⓘ</span>
-            Per Instagram/Facebook privati serve un file <strong>cookies.txt</strong> valido (Impostazioni → Percorsi).
+            <div>
+              In modalità <strong>Solo audio</strong> il file viene salvato in MP3 al bitrate impostato in Impostazioni → Download.<br>
+              Per Instagram/Facebook privati serve un file <strong>cookies.txt</strong> valido (Impostazioni → Percorsi).
+            </div>
           </div>
         </div>
 

webui/js/app.js

@@ -375,6 +375,17 @@ $("#videoBrowseBtn").addEventListener("click", async () => {
   }
 });
 
+let videoMode = "video";  // "video" | "audio"
+
+$$("#videoMode .seg-btn").forEach((b) => {
+  b.addEventListener("click", () => {
+    $$("#videoMode .seg-btn").forEach((x) => x.classList.remove("active"));
+    b.classList.add("active");
+    videoMode = b.dataset.mode;
+    $("#videoQualityField").style.display = videoMode === "audio" ? "none" : "";
+  });
+});
+
 $("#videoDownloadBtn").addEventListener("click", async () => {
   const url = $("#videoUrlInput").value.trim();
   if (!url) {
@@ -396,6 +407,7 @@ $("#videoDownloadBtn").addEventListener("click", async () => {
     urls: [url],
     output_dir: state.videoOutputDir,
     quality: $("#videoQuality").value,
+    audio_only: videoMode === "audio",
   });
   if (!res.ok) {
     toast(res.error || "Errore", "error");