Docs: Enhance feature enable/disable filter documentation with implementation details

[huzaifaalmesbah]

Description

Enhances the documentation for the ai_feature_{$feature_id}_enabled filter to provide better understanding of the feature enable/disable system.

Changes

• docs/DEVELOPER_GUIDE.md:
  • Added "How It Works" section explaining the internal flow
  • Added code references showing where the filter is implemented
  • Included more practical use case examples
  • Added explanation of when and why to use the filter

Why This Change?

The current documentation shows usage examples but doesn't adequately explain:

• Where the filter is defined in the codebase
• How the feature initialization flow works
• Real-world scenarios where this filter would be useful

This improvement helps developers understand not just what the filter does, but how it works and when to use it.

Type of Change

• Bug fix
• Documentation update
• New feature
• Enhancement

Testing

• Documentation is clear and accurate
• Code references are correct
• Examples are tested and working

Related Issues

Closes #68

[github-actions]

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Co-authored-by: huzaifaalmesbah <huzaifaalmesbah@git.wordpress.org>
Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
Co-authored-by: mindctrl <mindctrl@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.89%. Comparing base (3ca3e23) to head (128aebe).
⚠️ Report is 11 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop      #69   +/-   ##
==========================================
  Coverage      46.89%   46.89%           
  Complexity       208      208           
==========================================
  Files             19       19           
  Lines           1271     1271           
==========================================
  Hits             596      596           
  Misses           675      675           

Flag	Coverage Δ
unit	46.89% <ø> (ø)

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