Harden package metadata normalization

[Widthdom]

Summary

• Cap CodeIndex.PackageNormalize ZIP entry count, declared entry sizes, total uncompressed size, XML text size, and actual inflated read budgets before rewriting packages.
• Reject unsafe ZIP entry names before CreateEntry, including absolute paths, drive roots, traversal, backslashes, empty segments, and normalized duplicate destination names.
• Update release-package documentation and add security changelog fragments for both issues.

Validation

• Tests added or updated for changed behavior.
• dotnet build
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter "FullyQualifiedName~ReleaseWorkflowTests"
• dotnet test --no-build (full suite; run before the final adversarial-review follow-up commits)
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet format CodeIndex.sln --verify-no-changes
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json
• Codex adversarial review: No blocking/actionable issues found.

Documentation and changelog

• Documentation updated: DEVELOPER_GUIDE.md
• Changelog fragments added under changelog.d/unreleased/:
  • changelog.d/unreleased/2892.security.md
  • changelog.d/unreleased/2894.security.md
• Fragments follow .codex/workflows/changelog-fragment.md for category, issue front matter, and bilingual sections.

Issues

Fixes #2892
Fixes #2894

Follow-up issues

• None