Improve open-source project readiness and compliance

[mckaragoz]

Summary

Improve UltimateAuth's open-source infrastructure, build reproducibility, package metadata, and repository compliance to support long-term maintainability and community growth.

Scope

• Verify deterministic and reproducible NuGet builds.
• Validate Source Link, debugging symbols, and package metadata.
• Review third-party dependency licensing and copyright attribution.
• Strengthen release validation and repository security practices.
• Refine existing contribution and project documentation where necessary.

Notes

This PR focuses on project infrastructure and open-source quality standards.

No authentication behavior, public APIs, or architectural contracts are intended to change.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.98%. Comparing base (4d8c517) to head (054b7d2).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #84      +/-   ##
==========================================
+ Coverage   85.97%   85.98%   +0.01%     
==========================================
  Files         660      660              
  Lines       18275    18275              
  Branches     2249     2249              
==========================================
+ Hits        15712    15714       +2     
+ Misses       1811     1810       -1     
+ Partials      752      751       -1     

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