Index Unificati/Commerciali, merge cleanup buttons, report unmatched components

- Add 'Unificati' and 'Commerciali' as indexed root folders alongside the
  existing four, updating Indexer.CartelleRadice and the docs.
- Replace the separate "Pulisci cartella raw" / "Pulisci cartella step"
  buttons with a single "Pulisci raw e step" that clears both under one
  confirmation; falls back to a folder picker when no path is known yet
  in the session instead of staying disabled.
- "Trova componenti referenziati" now also writes a persistent summary
  (PRT/sub-assemblies found and copied, codes not found) to the main
  window's status line, not just the popup dialog, and reports clearly
  when no database is loaded instead of failing silently.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CadSearchGui/Indexer.cs

@@ -18,7 +18,7 @@ public sealed record ScanProgress(
 
 public static class Indexer
 {
-    public static readonly string[] CartelleRadice = { "__Accessori", "__B.end", "__Corpi", "__Fondi" };
+    public static readonly string[] CartelleRadice = { "__Accessori", "__B.end", "__Corpi", "__Fondi", "Unificati", "Commerciali" };
 
     private static readonly Regex FilenameRegex =
         new(@"^(?<codice>.+)\.(?<tipo>[A-Za-z0-9]+)\.(?<versione>\d+)$", RegexOptions.Compiled);