Add explicit working folder; rename project from CadSearchGui to PrepStep

Working folder (phase 1): CSV/raw/step/step_finali all used to live split
across two different implicit locations (CSV in the "repo root" found by
walking up for CLAUDE.md, raw/step next to the input distinta file) with
neither shown to the user. That repo-root lookup also silently breaks once
the app runs as a standalone published exe on a machine with no repo/
CLAUDE.md at all. Replaced both with one explicit "cartella di lavoro",
auto-suggested (last used, remembered the same way as the DB path) and
changeable from phase 1, with no dependency on any repo marker file.

Rename: CadSearchGui was the working name from before the app had a
product identity; renamed folders, csproj files, namespace and the
AppData settings folder to PrepStep throughout, matching the exe name
already in use. Product-facing name stays "Cevolani StepPrep".

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

PrepStep/ProgressoComponentiForm.cs

@@ -0,0 +1,37 @@
+namespace PrepStep;
+
+public sealed class ProgressoComponentiForm : Form
+{
+    private readonly Label _lbl = new();
+    private readonly ProgressBar _bar = new();
+
+    public ProgressoComponentiForm()
+    {
+        Text = "Ricerca componenti referenziati in corso...";
+        FormBorderStyle = FormBorderStyle.FixedDialog;
+        StartPosition = FormStartPosition.CenterParent;
+        MinimizeBox = false;
+        MaximizeBox = false;
+        ControlBox = false;
+        ClientSize = new Size(400, 88);
+
+        _lbl.Text = "Preparazione...";
+        _lbl.AutoSize = true;
+        _lbl.Location = new Point(16, 16);
+
+        _bar.Location = new Point(16, 44);
+        _bar.Size = new Size(368, 24);
+        _bar.Minimum = 0;
+        _bar.Maximum = 100;
+
+        Controls.Add(_lbl);
+        Controls.Add(_bar);
+    }
+
+    public void Aggiorna(int fatti, int totale)
+    {
+        int percento = totale > 0 ? (int)Math.Clamp(100.0 * fatti / totale, 0, 100) : 0;
+        _bar.Value = percento;
+        _lbl.Text = $"{fatti} / {totale} componenti analizzati ({percento}%)";
+    }
+}