Fix main CI duplicate request token declaration

[Widthdom]

Summary

• Remove the duplicate requestToken local declaration in MCP status handling that broke Release builds after Fix cancellation, heartbeat, and LSP symbol budget issues #3854 merged.

CI Root Cause

• Build and Test / build (windows-latest, net9.0) failed with CS0128: A local variable or function named 'requestToken' is already defined in this scope at src/CodeIndex/Mcp/McpToolHandlers.cs(3180,17).
• CodeQL / Analyze (csharp) failed for the same build error during its solution build.

Validation

• dotnet restore CodeIndex.sln --locked-mode
• dotnet build tests/CodeIndex.Tests/CodeIndex.Tests.csproj --configuration Release --framework net9.0 --no-restore -p:UseSharedCompilation=false
• dotnet build CodeIndex.sln --configuration Release --no-restore -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --configuration Release --no-build --filter ToolsCall_StatusUpdateCheck_UsesRequestCancellationToken_Issue3658 -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check
• git diff --check origin/main...HEAD
• dotnet build -p:UseSharedCompilation=false
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll index . --json
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json

No changelog fragment: this is a CI build repair for an already-merged change and does not alter user-visible behavior.

Refs #3854