fix: Correct inverted required field logic in schema generator

[nan1888]

Fixes #1610

Problem:

• Schema generator had inverted logic for 'required' field
• Fields WITH defaults were marked as required
• Fields WITHOUT defaults were not marked as required

Solution:

• Changed required: has_default to required: not has_default

Impact:

• Config schema will now correctly identify required fields

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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[Wanbogang]

Bug confirmed: Inverted logic in required field detection.

Fix verified:

• Before: required = has_default (fields with defaults marked required)
• After: required = not has_default (correct logic)

Logic validated:

• Field without default → required = True
• Field with default → required = False