Remove "defaults" section from main JSON schema

[Copilot]

This PR removes the defaults section from the main workflow schema (main_workflow_schema.json). This section was intended for GitHub Actions workflow defaults (default shell and working directory) but was not being used in any workflows and added unnecessary complexity to the schema.

Changes

Schema Updates:

• Removed the top-level defaults property definition from main_workflow_schema.json (lines 1073-1094)
• Removed the $ref reference to defaults within the jobs section (lines 1197-1199)

Code Updates:

• Removed defaults from PriorityJobFields constant in pkg/constants/constants.go
• Removed test cases for the defaults field in pkg/parser/schema_test.go

Documentation:

• Auto-generated schema documentation updated to remove the defaults section

Validation

The schema now correctly rejects workflows that attempt to use the defaults field:

$ ./gh-aw compile test-workflow.md
✗ failed to parse workflow file: error: Unknown property: defaults. 
Did you mean one of: imports, runtimes, services

Important Note: The defaults network access mode (e.g., network: defaults) is a completely separate feature and remains unchanged. This PR only removes the GitHub Actions workflow defaults section that was not being utilized.

Testing

• ✅ All unit tests pass
• ✅ All integration tests pass
• ✅ All 67 workflows in the repository compile successfully
• ✅ Schema validation correctly rejects the removed field
• ✅ Network "defaults" mode still functions properly
• ✅ Binary rebuilt with embedded schema changes

Original prompt

Remove "defaults" section from the main json schema.

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[github-actions]

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