fix(security): harden option maps against prototype pollution

[ghiscoding]

Summary

• Normalize API options with Object.create(null).
• Harden getDestinationPath against inherited properties.
• Use a null-prototype CLI option map.
• Add regression tests for prototype-polluted options.

Validation

• Biome checks passed
• TypeScript build passed
• 61 tests passed

LLM model

Implemented and reviewed with OpenAI GPT-5.6 Luna

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (0ea37a8) to head (8151e66).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #93   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          200       206    +6     
  Branches        68        68           
=========================================
+ Hits           200       206    +6     

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