em 01: scaffold ExtractMethod tool + Demo fixture

- tools/ExtractMethod: net10.0 console app (Microsoft.CodeAnalysis.CSharp
  5.9.0, pinned latest stable). CLI: <file.cs> <startLine> <endLine>.
  Parses the file, builds a scratch compilation with refs from
  TRUSTED_PLATFORM_ASSEMBLIES, and reports how many whole statements the
  line range covers (clean error otherwise; exit codes: 0 ok, 1
  resolution error, 2 usage).
- Tooling/CompilationLoader: shared parse + compilation path for CLI and
  tests (tests exercise the exact loading path the CLI uses).
- Tooling/SelectionResolver: snaps a 1-based inclusive line range to
  whole statements in the enclosing method body block; boundary checks
  never split a statement; nested/blank-line ranges handled cleanly.
- tests/: ExtractMethod/Fixtures/Demo.cs checked-in fixture exercising
  every bucket of the parent spec (read-only local, written+read-later
  return, scratch local, param read, field+property access, indexer +
  method invocation, multi-statement range incl. a for-loop); excluded
  from project compilation, copied to output as data.
- Tests: Demo.cs compiles with no diagnostics; range 68..72 resolves to
  2 statements (LocalDeclarationStatement, ForStatement); AnalyzeDataFlow
  succeeds on the fixture's for-loop node; mid-statement range fails
  cleanly. 30/30 green.

tests/BeforeAfter.Tests/BeforeAfter.Tests.csproj

@@ -21,6 +21,19 @@
   <ItemGroup>
     <ProjectReference Include="..\..\src\Before\Before.csproj" />
     <ProjectReference Include="..\..\src\After\After.csproj" />
+    <ProjectReference Include="..\..\tools\ExtractMethod\ExtractMethod.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <!-- The ExtractMethod fixtures are DATA for the Roslyn tool, not source:
+         they are excluded from this project's compilation (the scratch
+         compilation gives the tool the exact checked-in text) and copied to
+         the output dir so tests can find them by path. -->
+    <Compile Remove="ExtractMethod\Fixtures\**\*.cs" />
+    <!-- Rebase the copy target to Fixtures/ in the output dir: the tool's
+         apphost (the Executable 'ExtractMethod') is copied here too, and a
+         folder named ExtractMethod/ would collide with that file. -->
+    <Content Include="ExtractMethod\Fixtures\**\*.cs" Link="Fixtures\%(RecursiveDir)%(Filename)%(Extension)" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
 
 </Project>