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/admin/settings.ts

@@ -24,6 +24,7 @@ export const GET: APIRoute = async () => {
     // Speicherverwaltung
     keep_sources: s.keep_sources, make_thumbnails: s.make_thumbnails, retention_days: s.retention_days,
     metadata_sidecar: s.metadata_sidecar, api_token: s.api_token,
+    picdrop_metadata_sidecar: s.picdrop_metadata_sidecar, nas_metadata_sidecar: s.nas_metadata_sidecar,
     // Rechte / Datenschutz / NSFW
     library_visibility: s.library_visibility, anonymous_generations: s.anonymous_generations,
     private_allowed: s.private_allowed, allow_nsfw: s.allow_nsfw,
@@ -43,10 +44,11 @@ export const PATCH: APIRoute = async ({ request }) => {
   if (b.nas_password) set('nas_password_enc', encrypt(String(b.nas_password)));
   if (b.generate_api_token) set('api_token', randomToken());
   const boolCols = ['keep_sources', 'make_thumbnails', 'nas_enabled', 'metadata_sidecar',
-    'anonymous_generations', 'private_allowed', 'allow_nsfw'];
+    'picdrop_metadata_sidecar', 'nas_metadata_sidecar', 'anonymous_generations', 'private_allowed', 'allow_nsfw'];
   for (const col of ['picdrop_host', 'picdrop_protocol', 'picdrop_port', 'picdrop_user', 'picdrop_base_path',
     'picdrop_default_gallery', 'default_dpi', 'default_crop_mode', 'concurrency', 'cricut_sheet_cm', 'monthly_budget', 'n8n_webhook_url',
     'keep_sources', 'make_thumbnails', 'retention_days', 'metadata_sidecar', 'api_token',
+    'picdrop_metadata_sidecar', 'nas_metadata_sidecar',
     'library_visibility', 'anonymous_generations', 'private_allowed', 'allow_nsfw',
     'nas_enabled', 'nas_host', 'nas_protocol', 'nas_port', 'nas_user', 'nas_base_path']) {
     if (col in b) {