Wrap exact-match help text

[Widthdom]

Summary

• Wrap the --exact, --exact-substring, and --exact-name help text into shorter continuation lines.
• Add focused usage-output coverage that keeps the exact-match option block within 80 columns.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter "FullyQualifiedName~ConsoleUiTests" -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false
• Adversarial review: No blocking/actionable issues found.

Documentation / Changelog

• Added changelog.d/unreleased/1426.fixed.md.

Follow-up candidates

• None.

Fixes #1426