Add Distinta Base import tab: parse .xls/.xml export to CSV with preview

Reads the ERP-exported "Distinta Base" file (SpreadsheetML XML or real
binary .xls/.xlsx via ExcelDataReader), extracts Componente/Descrizione,
writes a CSV and previews it in a new tab alongside the existing CAD
search. Also ignore the exported Excel/CSV files dropped in the repo root.

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

.gitignore

@@ -19,3 +19,9 @@ publish/
 
 # Stato locale degli strumenti agentici
 .claude/
+
+# File Excel/XML della Distinta Base (esportati dal gestionale) e il CSV generato
+/*.xls
+/*.xlsx
+/*.xls.xml
+/*.csv