feat: add booklet download button, remove pdfjs-dist dependency

- Add save/download button to booklet toolbar with native file dialog
- Add v2_booklet_save command to copy PDF to user-chosen location
- Remove pdfjs-dist npm package (replaced by MuPDF backend)
- Delete static/pdfjs/ files (~1.9MB: worker, WASM decoders, fallbacks)
- Add bookletDownload i18n keys to all 4 locales

src/lib/components/BookletViewer.svelte

@@ -2,7 +2,8 @@
   import { tick } from 'svelte';
   import { t } from 'svelte-i18n';
   import { invoke } from '@tauri-apps/api/core';
-  import { X, ChevronLeft, ChevronRight, ZoomIn, ZoomOut, Maximize, RotateCw } from 'lucide-svelte';
+  import { X, ChevronLeft, ChevronRight, ZoomIn, ZoomOut, Maximize, RotateCw, Download } from 'lucide-svelte';
+  import { save } from '@tauri-apps/plugin-dialog';
 
   interface PageSize {
     width: number;
@@ -174,6 +175,26 @@
     renderPage();
   }
 
+  async function downloadBooklet() {
+    if (!bookletLoaded) return;
+
+    const defaultName = title
+      ? `${title}.pdf`
+      : 'Booklet.pdf';
+
+    const dest = await save({
+      filters: [{ name: 'PDF', extensions: ['pdf'] }],
+      defaultPath: defaultName,
+    });
+    if (!dest) return;
+
+    try {
+      await invoke('v2_booklet_save', { dest });
+    } catch (err: any) {
+      console.error('[BookletViewer] Save error:', err);
+    }
+  }
+
   function handleKeydown(e: KeyboardEvent) {
     if (!isOpen) return;
 
@@ -270,6 +291,10 @@
         <button class="toolbar-btn" onclick={rotate} title={$t('album.bookletRotate')}>
           <RotateCw size={16} />
         </button>
+        <div class="toolbar-divider"></div>
+        <button class="toolbar-btn" onclick={downloadBooklet} title={$t('album.bookletDownload')} disabled={!bookletLoaded}>
+          <Download size={16} />
+        </button>
       </div>
       <div class="toolbar-right">
         <button class="toolbar-btn close-btn" onclick={onClose}>

src/lib/i18n/locales/de.json

@@ -233,7 +233,8 @@
     "bookletLoading": "Booklet wird geladen...",
     "bookletError": "Booklet konnte nicht geladen werden",
     "bookletFitWidth": "An Breite anpassen",
-    "bookletRotate": "Drehen"
+    "bookletRotate": "Drehen",
+    "bookletDownload": "Booklet speichern"
   },
   "artist": {
     "albums": "Alben",

src/lib/i18n/locales/en.json

@@ -245,7 +245,8 @@
     "bookletLoading": "Loading booklet...",
     "bookletError": "Could not load booklet",
     "bookletFitWidth": "Fit to width",
-    "bookletRotate": "Rotate"
+    "bookletRotate": "Rotate",
+    "bookletDownload": "Save booklet"
   },
   "artist": {
     "albums": "Albums",

src/lib/i18n/locales/es.json

@@ -245,7 +245,8 @@
     "bookletLoading": "Cargando libreto...",
     "bookletError": "No se pudo cargar el libreto",
     "bookletFitWidth": "Ajustar al ancho",
-    "bookletRotate": "Rotar"
+    "bookletRotate": "Rotar",
+    "bookletDownload": "Guardar booklet"
   },
   "artist": {
     "albums": "Álbumes",

src/lib/i18n/locales/fr.json

@@ -233,7 +233,8 @@
     "bookletLoading": "Chargement du livret...",
     "bookletError": "Impossible de charger le livret",
     "bookletFitWidth": "Ajuster à la largeur",
-    "bookletRotate": "Pivoter"
+    "bookletRotate": "Pivoter",
+    "bookletDownload": "Enregistrer le livret"
   },
   "artist": {
     "albums": "Albums",