Cap report schema summary work

[Widthdom]

Summary

• Cap cdidx report --db schema table enumeration at 64 entries and omit additional tables from schema.txt.
• Cap displayed table names at 96 characters and report bounded row counts with a 1000-row scan limit per table.
• Update report documentation and add a bilingual changelog fragment.

Validation

• dotnet format CodeIndex.sln --verify-no-changes
• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false
• dotnet build
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release -p:UseSharedCompilation=false --filter FullyQualifiedName~ReportCommandRunnerTests
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release -p:UseSharedCompilation=false --filter FullyQualifiedName~ExtractorPluginRegistryTests.LoadPluginAssemblies_RetainsCapDiagnosticWhenCandidatesAlsoFailToLoad
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json

Full dotnet test CodeIndex.sln -c Release -p:UseSharedCompilation=false was attempted, but I stopped it after a long no-output run. It had reported one unrelated ExtractorPluginRegistryTests regex-timeout failure first; that specific test passed on isolated rerun for both target frameworks.

Documentation / Changelog

• Updated USER_GUIDE.md report bundle text in English and Japanese.
• Added changelog.d/unreleased/3146.security.md.

Review

Adversarial review found one documentation wording issue (no user content was too strong because schema summaries still include table names). That was fixed; no blocking/actionable issues remained after re-review.

Follow-up Candidates

• None.

Fixes #3146