Show a progress dialog while resolving referenced components

"Trova componenti referenziati" ran the recursive BFS synchronously on the
UI thread with no feedback. Runs it on a background task instead and shows
a modal dialog with a percentage bar, updated as each .asm in the queue is
processed.

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

CadSearchGui/ProgressoComponentiForm.cs

@@ -0,0 +1,37 @@
+namespace CadSearchGui;
+
+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}%)";
+    }
+}