fix(style-guides): simplify dual-platform models with optional groupId

[YHorodyskyi]

fix(style-guides): simplify dual-platform models with optional groupId

Summary

Simplifies Style Guides API models to use a single interface with optional groupId instead of separate Crowdin/Enterprise interfaces. Aligns with the pattern used in machineTranslation and other dual-platform modules.

Changes

• StyleGuide: Added optional groupId?: number (Enterprise only) instead of StyleGuideEnterprise interface
• CreateStyleGuideRequest: Added optional groupId?: number | null (Enterprise only) instead of CreateStyleGuideEnterpriseRequest
• Method signatures: Removed union types (StyleGuide | StyleGuideEnterprise), now return StyleGuide directly
• Tests: Updated assertions to use direct groupId access

Rationale

Style Guides API serves both Crowdin and Crowdin Enterprise. The only platform-specific difference is groupId (Enterprise). Using optional groupId keeps the API surface simpler and consistent.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.85%. Comparing base (8595f57) to head (0e4cbac).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #639   +/-   ##
=======================================
  Coverage   89.85%   89.85%           
=======================================
  Files          41       41           
  Lines        2126     2126           
  Branches      254      254           
=======================================
  Hits         1910     1910           
  Misses         82       82           
  Partials      134      134           

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