feat: per-source .md sidecar toggles, Picdrop folder-list diagnostic, fast JPEG fullscreen preview + thumb-first, thumbnail backfill

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNQ8ghPfzAfsyVYd6HgFb6

src/components/LibraryApp.tsx

@@ -249,10 +249,13 @@ export default function LibraryApp() {
       )}
       {saveView && (
         <div className="lupe" onClick={() => setSaveView(null)}>
-          <img className="saveimg" src={`/api/items/${saveView.id}/file`} alt={saveView.filename || ''} onClick={(e) => e.stopPropagation()} />
+          <div className="savewrap" onClick={(e) => e.stopPropagation()}>
+            <img className="saveimg blur" src={`/api/items/${saveView.id}/file?thumb=1`} alt="" />
+            <img className="saveimg full" src={`/api/items/${saveView.id}/file?preview=1`} alt={saveView.filename || ''} />
+          </div>
           <div className="save-fuss" onClick={(e) => e.stopPropagation()}>
             <span>📱 iPhone/iPad: lange auf das Bild tippen → <b>„In Fotos sichern"</b>.</span>
-            <a className="mini stark" href={`/api/items/${saveView.id}/file?download=1`}>Als Datei herunterladen</a>
+            <a className="mini stark" href={`/api/items/${saveView.id}/file?download=1`}>Original als Datei (.png)</a>
             <button className="mini" onClick={() => setSaveView(null)}>Schließen</button>
           </div>
         </div>
@@ -309,7 +312,10 @@ function LibStyles() {
     .tagmenu button{display:flex;align-items:center;gap:8px;background:none;border:none;text-align:left;padding:7px 9px;cursor:pointer;font-family:inherit;font-size:13px;border-radius:4px;color:var(--ink);}
     .tagmenu button:hover{background:var(--paper);}
     .tagmenu .flag{font-size:15px;}
+    .savewrap{position:relative;max-width:94vw;max-height:78vh;display:flex;}
     .saveimg{max-width:94vw;max-height:78vh;border-radius:4px;display:block;}
+    .saveimg.blur{filter:blur(8px);position:absolute;inset:0;width:100%;height:100%;object-fit:contain;}
+    .saveimg.full{position:relative;z-index:1;}
     .save-fuss{display:flex;flex-direction:column;align-items:center;gap:10px;color:#EAEAE3;font-size:13.5px;text-align:center;max-width:90vw;}
     .fassung{position:absolute;bottom:6px;right:6px;background:rgba(22,21,15,.7);color:#fff;font-family:var(--font-mono);font-size:9px;padding:2px 7px;border-radius:20px;}
     .varianten{display:flex;gap:5px;margin-top:6px;overflow-x:auto;}