[task] Add required fields array to main_workflow_schema.json

[github-actions]

Objective

Add the "required": ["on"] field to the main workflow schema to enforce that all workflows must have a trigger.

Context

This addresses Issue #1 from discussion #2969. Currently, all three schemas (main_workflow_schema.json, included_file_schema.json, mcp_config_schema.json) have zero required fields defined, yet 100% of production workflows (67/67) use the on: field. The schema should reflect this implicit requirement.

Approach

1. Open pkg/parser/schemas/main_workflow_schema.json
2. Add a "required" array at the root level with "on" as the first entry
3. Update the schema description to clarify that on: is mandatory

Files to Modify

• pkg/parser/schemas/main_workflow_schema.json - Add required fields array

Example Change

{
  "$schema": "(redacted)#",
  "title": "Agentic Workflow",
  "type": "object",
  "required": ["on"],
  "properties": {
    "on": {
      ...
    }
  }
}

Acceptance Criteria

• Schema includes "required": ["on"] at root level
• Schema validation rejects workflows without on: field
• Existing workflows continue to pass validation
• Run make build and make test successfully
  Related to [Schema Consistency] 🔍 Schema Consistency Check - Required Fields & Error Documentation Gap (Nov 2, 2025) #2969

AI generated by Plan Command for discussion #2969