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/pages/api/items/[id]/file.ts

@@ -1,4 +1,5 @@
 import type { APIRoute } from 'astro';
+import sharp from 'sharp';
 import { one } from '../../../../lib/db';
 import { getObject } from '../../../../lib/storage';
 
@@ -28,13 +29,19 @@ export const GET: APIRoute = async ({ params, url, locals }) => {
     : item?.result_path;
   if (!path) return new Response('Nicht gefunden', { status: 404 });
   try {
-    const buf = await getObject(path);
+    let buf = await getObject(path);
     const download = q.get('download') === '1';
-    const isWebp = path.endsWith('.webp');
+    let contentType = path.endsWith('.webp') ? 'image/webp' : 'image/png';
+    // Schnelle Vollbild-Vorschau: nicht-transparente Ergebnisse als JPEG (deutlich kleiner,
+    // schneller auf Mobil) — reicht fürs „In Fotos sichern". Der PNG-Download bleibt unverändert.
+    if (q.get('preview') === '1' && !download && !item?.has_alpha) {
+      try { buf = await sharp(buf, { failOn: 'none' }).jpeg({ quality: 90, mozjpeg: true }).toBuffer(); contentType = 'image/jpeg'; }
+      catch { /* Fallback: Original */ }
+    }
     return new Response(buf, {
       headers: {
-        'Content-Type': isWebp ? 'image/webp' : 'image/png',
-        'Cache-Control': 'private, max-age=300',
+        'Content-Type': contentType,
+        'Cache-Control': 'private, max-age=600',
         ...(download ? { 'Content-Disposition': `attachment; filename="${item.filename || 'klarbild.png'}"` } : {}),
       },
     });