Cap runtime environment override values

[Widthdom]

Summary

• Cap GitHub suggestion submission timeout overrides to 1-300 seconds.
• Cap suggestion retention age/count overrides, including .cdidxrc.json validation.
• Cap global log rotation size overrides from CLI and environment variables.
• Cap SQLite cache/mmap performance environment overrides.

Validation

• dotnet build -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter FullyQualifiedName~GitHubIssueReporterTests -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter FullyQualifiedName~SuggestionStoreTests -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter FullyQualifiedName~CdidxConfigFileTests -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter FullyQualifiedName~GlobalToolLogTests -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter FullyQualifiedName~ProgramRunnerTests.Run_LogMaxSizeMbAboveMaximum_ReturnsInvalidArgument -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build --filter FullyQualifiedName~DatabaseTests.Constructor_ -p:UseSharedCompilation=false
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json
• Adversarial review: No blocking/actionable issues found.

Full-suite note: dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --no-build -p:UseSharedCompilation=false failed during validation with ReferenceExtractorTests.Extract_SQL_DeleteUsingMixedTableAndTempSourcesAfterComma_AreNotTreatedAsComments; the same test passed when filtered directly in both target frameworks. This order-dependent suite failure is already tracked by #2947.

Follow-up Issues

• Search queries that look like global log flags are parsed as options #2955

Fixes #2916
Fixes #2915
Fixes #2890
Fixes #2889