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/PrepStep.csproj

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <UseWindowsForms>true</UseWindowsForms>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <ApplicationHighDpiMode>PerMonitorV2</ApplicationHighDpiMode>
+    <ApplicationIcon>app.ico</ApplicationIcon>
+    <!-- Nome tecnico (cartella/csproj/namespace) e nome del file .exe pubblicato: PrepStep.
+         Il nome prodotto mostrato all'utente ("Cevolani StepPrep") resta separato, sotto. -->
+    <AssemblyTitle>Cevolani StepPrep</AssemblyTitle>
+    <Product>Cevolani StepPrep</Product>
+    <Company>Cevolani</Company>
+    <Version>0.1.0</Version>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Data.Sqlite" Version="10.0.12" />
+    <PackageReference Include="ExcelDataReader.DataSet" Version="3.9.0" />
+    <PackageReference Include="System.Text.Encoding.CodePages" Version="9.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute">
+      <_Parameter1>PrepStep.Tests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
+</Project>