[task] Refactor CopilotEngine to use unified MCPConfigRenderer

[github-actions]

Objective

Update pkg/workflow/copilot_engine.go to use the unified MCPConfigRenderer instead of duplicated rendering functions.

Context

CopilotEngine currently has 4 duplicated MCP rendering functions with Copilot-specific fields (e.g., includeCopilotFields). These should be replaced with calls to the unified renderer. Related to #3942.

Approach

1. Update copilot_engine.go to use NewMCPConfigRenderer() with Copilot-specific options
2. Replace these functions with unified renderer calls:
   • renderGitHubCopilotMCPConfig() → Use renderer.RenderGitHubMCP()
   • renderPlaywrightCopilotMCPConfig() → Use renderer.RenderPlaywrightMCP()
   • renderSafeOutputsCopilotMCPConfig() → Use renderer.RenderSafeOutputsMCP()
   • renderAgenticWorkflowsCopilotMCPConfig() → Use renderer.RenderAgenticWorkflowsMCP()
3. Configure renderer options with IncludeCopilotFields: true
4. Update tests to verify Copilot-specific behavior is preserved

Files to Modify

• pkg/workflow/copilot_engine.go - Update to use unified renderer
• pkg/workflow/copilot_engine_test.go - Update tests if needed

Acceptance Criteria

• All 4 Copilot MCP rendering functions replaced with unified renderer calls
• CopilotEngine configured with IncludeCopilotFields: true option
• All existing tests pass without modification to expected behavior
• Code compiles without errors
• No duplicate rendering logic remains in copilot_engine.go
• Copilot-specific fields are correctly included in MCP configuration output
  Related to [refactor] 🔧 Semantic Function Clustering Analysis: Refactoring Opportunities #3942

AI generated by Plan Command for #3942