fix: restore zero-warning CodeQL baseline

[savasp-agent]

Summary

• restore the portable CodeQL warning/error baseline to zero after Regenerate the Apache AGE compliance report from a strict certification run #393 found 25 warning-level results on the release candidate
• make the AGE complex-mutation plan invariant explicit and preserve nullable constraint values without redundant casts
• remove redundant test/serialization conversions and consume documentation-snippet results meaningfully
• retain two expression-tree casts that C# requires, with narrow CodeQL suppressions

Validation

• dotnet build --configuration Debug: passed, 0 warnings/errors
• affected fast projects: 1,887 tests passed
• full fast lane: 8 projects / 2,526 tests passed
• dotnet format cvoya-graph.sln --verify-no-changes --no-restore --verbosity minimal: passed
• portable CodeQL 2.26.1: Actions 0 results; C# 724/724 files, 132 notes and 0 warnings/errors; Ruby 0 results
• pre-push Release build and formatting gate: passed, 0 warnings/errors

After this merges, #393 must restart strict certification from the new origin/main SHA and discard its evidence against adea65e2.

Closes #534.

[savasp-agent]

Fixed the documentation CI failure in 58c9ec5 by keeping the new result-use statements outside the checked snippet markers. Verification: ./scripts/validate-documentation.sh Debug passed locally, the pre-push Release build/format gate passed, and the replacement hosted Build and Validate Documentation job passed (run 29998524382).