[codex] Add Claude Sonnet 5 support

[TheFellow]

Summary

• add Claude Sonnet 5 to the model catalog, aliases, defaults, and generated model conformance matrix
• update Anthropic reasoning request shape so Sonnet 5 uses adaptive thinking
• add Sonnet 5 coding-agent conformance coverage
• replace retired gemini-2.0-flash live-test selectors with gemini-2.5-flash
• bump the CLI minor version to 0.18.0 and reinstall locally

Validation

• make format-check
• make lint
• make analyze
• make install
• /Users/Ryan.Harris/bin/attractor --version -> 0.18.0
• dotnet test tests/UnifiedLlm.Tests/UnifiedLlm.Tests.fsproj --no-restore --filter "FullyQualifiedName!~LiveApiTests"
• dotnet test tests/UnifiedLlm.Tests/UnifiedLlm.Tests.fsproj --no-restore --filter "FullyQualifiedName~LiveApiTests"
• dotnet test tests/Attractor.Tests/Attractor.Tests.fsproj --no-restore --filter "FullyQualifiedName~LiveApiTests"
• dotnet test tests/CodingAgent.Tests/CodingAgent.Tests.fsproj --no-restore --filter "FullyQualifiedName~LiveApiTests"
• live Sonnet 5 conformance smoke tests for model and coding-agent paths