Add raw-folder step, redesign UI, remember last DB path, add README

- Split the import flow into explicit steps: import/preview CSV, then a
  separate "Crea cartella raw" button that looks up CAD paths and copies
  matched files into raw/ next to the source distinta file.
- Redesign the top panel with grouped, auto-sized sections (database vs.
  import) instead of hand-tuned row heights, fixing overlap/clipping bugs;
  style the primary action button and polish the results grid.
- Remember the last successfully loaded database path in
  %AppData%\CadSearchGui\ultimo_db.txt so it reloads automatically on
  future launches regardless of the working directory.
- Ignore the /step/ working folder.
- Add a README with build/run/publish instructions and project overview.

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

.gitignore

@@ -20,8 +20,11 @@ publish/
 # Stato locale degli strumenti agentici
 .claude/
 
-# File Excel/XML della Distinta Base (esportati dal gestionale) e il CSV generato
+# File Excel/XML della Distinta Base (esportati dal gestionale), il CSV generato
+# e la cartella con le copie dei file CAD trovati
 /*.xls
 /*.xlsx
 /*.xls.xml
 /*.csv
+/raw/
+/step/