Add cache cap, playlist export/import, yt-dlp build flag

Cache cap: dropdown setting (no limit / 1/2/5/10 GB) stored in
settings.cacheCap (actual eviction handled by native side).
Export: downloads playlists as JSON via Blob. Import: file reader
merges new playlists by id. yt-dlp: feature gate 'embed-ytdlp'
(default on), skip with --no-default-features for faster debug builds.

Files:
- frontend/app.js: exportPlaylists/importPlaylists, cache cap select
- src-tauri/Cargo.toml: [features] embed-ytdlp
- src-tauri/src/main.rs: #[cfg(feature = embed-ytdlp)] guards

frontend/app.js

@@ -850,10 +850,32 @@ async function renderSettings() {
         <span>Storage used</span>
         <span id="cacheTotal" class="set-stat">…</span>
       </div>
+      <label class="set-row">
+        <span>
+          Cache size limit
+          <small>Auto-evict oldest files when cache exceeds this.</small>
+        </span>
+        <select id="cacheCapSelect" class="set-select">
+          <option value="0">No limit</option>
+          <option value="1073741824">1 GB</option>
+          <option value="2147483648">2 GB</option>
+          <option value="5368709120">5 GB</option>
+          <option value="10737418240">10 GB</option>
+        </select>
+      </label>
       <div class="set-actions">
         <button id="clearCacheBtn" class="btn danger">Clear all cached videos</button>
       </div>
       <div id="cacheList" class="cache-list"></div>
+    </div>
+
+    <div class="set-group">
+      <div class="set-group-title">Playlists</div>
+      <div class="set-row" style="border:none;gap:8px;flex-wrap:wrap">
+        <button id="exportBtn" class="btn">Export playlists</button>
+        <button id="importBtn" class="btn">Import playlists</button>
+        <input id="fileInput" type="file" accept=".json" style="display:none" />
+      </div>
     </div>`;
 
   c.appendChild(wrap);
@@ -930,6 +952,19 @@ async function renderSettings() {
     const t = $('cacheTotal');
     if (t) t.textContent = 'Offline cache not available in this build';
   }
+
+  // ---- Cache cap ----
+  const capSel = $('cacheCapSelect');
+  capSel.value = String(data.settings.cacheCap || 0);
+  capSel.addEventListener('change', (e) => {
+    data.settings.cacheCap = parseInt(e.target.value) || 0;
+    persist();
+  });
+
+  // ---- Export / Import playlists ----
+  $('exportBtn').addEventListener('click', exportPlaylists);
+  $('importBtn').addEventListener('click', () => $('fileInput').click());
+  $('fileInput').addEventListener('change', importPlaylists);
 }
 
 function renderCard(v, index, list) {
@@ -1010,6 +1045,43 @@ function render() {
 // ============================================================================
 // Playlists
 // ============================================================================
+function exportPlaylists() {
+  const json = JSON.stringify(data.playlists, null, 2);
+  const blob = new Blob([json], { type: 'application/json' });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = `ytplayer-playlists-${new Date().toISOString().slice(0, 10)}.json`;
+  a.click();
+  URL.revokeObjectURL(url);
+  toast('Playlists exported');
+}
+function importPlaylists(e) {
+  const file = e.target.files?.[0];
+  if (!file) return;
+  const reader = new FileReader();
+  reader.onload = (ev) => {
+    try {
+      const imported = JSON.parse(ev.target.result);
+      if (!Array.isArray(imported)) throw new Error('Invalid format');
+      // Merge: skip duplicates by id, add new ones
+      const existingIds = new Set(data.playlists.map((p) => p.id));
+      for (const pl of imported) {
+        if (pl.id && pl.name && Array.isArray(pl.videos) && !existingIds.has(pl.id)) {
+          data.playlists.push(pl);
+          existingIds.add(pl.id);
+        }
+      }
+      persist();
+      renderSidebar();
+      toast(`Imported ${imported.length} playlist(s)`);
+    } catch (err) {
+      toast('⚠ Failed to import: ' + err.message);
+    }
+  };
+  reader.readAsText(file);
+  e.target.value = ''; // allow re-import of same file
+}
 function openCardMenu(video) {
   const inPlaylistView = view.type === 'playlist';
   const body = document.createElement('div');