Precompute search snippet query context

[Widthdom]

Summary

• Added a prepared search snippet query context so normalized query text and tokens are computed once per search command.
• Updated CLI and MCP compact search result formatting to reuse the prepared context across results.
• Kept C# verbatim-name normalization language-aware when one context is reused across mixed-language results.

Validation

• dotnet build CodeIndex.sln
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter "FullyQualifiedName~SearchSnippetFormatterTests"
• dotnet format CodeIndex.sln --verify-no-changes --no-restore
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json

Attempted dotnet test CodeIndex.sln; it produced no final summary after more than 30 minutes in the local environment, so it was stopped after the targeted tests and build had passed.

Documentation / Changelog

• Added changelog.d/unreleased/3089.internal.md.
• No docs update: compact output shape and user-facing behavior are unchanged.

Review

No blocking/actionable issues found in adversarial review.

Follow-up Candidates

None.

Fixes #3089