feat: duplicate detection + original URL in description

- Add original recipe URL to Mealie description (appended after blank line)
- Check for duplicate recipes on scrape (match orgURL or URL in description)
- Show warning with link to existing recipe if duplicate found
- User can still import anyway (warning only, not blocking)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/base.html

@@ -162,6 +162,7 @@
         .text-dim { color: var(--text-dim); }
         .text-success { color: var(--success); }
         .text-danger { color: var(--danger); }
+        .text-warning { color: var(--warning); }
         .flex { display: flex; gap: 0.75rem; align-items: center; }
         .flex-wrap { flex-wrap: wrap; }
         .grow { flex: 1; }