refactor: Zod-based config loader

[fabiovincenzi]

Replace JSON-Schema with Zod for config validation and default injection
Add typed config export, loadConfig(), validate() and setConfigFile()
Update index.ts to use the new loader and pass the validated config.

[netlify]

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Name	Link
🔨 Latest commit	fa83356
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[codecov]

Codecov Report

Attention: Patch coverage is 80.76923% with 5 lines in your changes missing coverage. Please review.

Project coverage is 48.08%. Comparing base (fc6f166) to head (fa83356).

Files with missing lines	Patch %	Lines
src/config/file.ts	50.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #998      +/-   ##
==========================================
- Coverage   48.51%   48.08%   -0.44%     
==========================================
  Files          51       52       +1     
  Lines        2092     2111      +19     
  Branches      241      241              
==========================================
  Hits         1015     1015              
- Misses       1040     1052      +12     
- Partials       37       44       +7     

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