Add wizard UI, general-assembly resolution, and test suite

Restructure Form1 into a sequential wizard (database -> import -> raw ->
recursive component resolution -> completeness/STEP report), fix
case-sensitivity bugs in codice/tipo_file lookups and a word-boundary gap
in the assembly scanner that missed _D100-style sub-assembly references,
and treat the distinta's general assembly as an ordinary CSV row (derived
from the DBP_<codice>_<timestamp> filename) instead of special-casing it
throughout. Also adds CadSearchGui.Tests (xUnit) covering the scanner,
filename parsing, and the case-insensitive DB lookup behavior.

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

CadSearchGui/CadSearchGui.csproj

@@ -14,4 +14,10 @@
     <PackageReference Include="System.Text.Encoding.CodePages" Version="9.0.0" />
   </ItemGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute">
+      <_Parameter1>CadSearchGui.Tests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
 </Project>