fix: convert partyModeWorkflow to skill ref, drop unused task refs

- partyModeWorkflow now uses skill:bmad-party-mode (it is a skill)
- remove advancedElicitationTask and partyModeWorkflow from steps 1/4
  where they are not referenced in the body

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/bmm/workflows/3-solutioning/bmad-create-epics-and-stories/steps/step-01-validate-prerequisites.md

@@ -6,10 +6,6 @@ description: 'Validate required documents exist and extract all requirements for
 nextStepFile: './step-02-design-epics.md'
 outputFile: '{planning_artifacts}/epics.md'
 epicsTemplate: '../templates/epics-template.md'
-
-# Task References
-advancedElicitationTask: 'skill:bmad-advanced-elicitation'
-partyModeWorkflow: '{project-root}/_bmad/core/workflows/bmad-party-mode/workflow.md'
 ---
 
 # Step 1: Validate Prerequisites and Extract Requirements

src/bmm/workflows/3-solutioning/bmad-create-epics-and-stories/steps/step-02-design-epics.md

@@ -8,7 +8,7 @@ outputFile: '{planning_artifacts}/epics.md'
 
 # Task References
 advancedElicitationTask: 'skill:bmad-advanced-elicitation'
-partyModeWorkflow: '{project-root}/_bmad/core/workflows/bmad-party-mode/workflow.md'
+partyModeWorkflow: 'skill:bmad-party-mode'
 ---
 
 # Step 2: Design Epic List

src/bmm/workflows/3-solutioning/bmad-create-epics-and-stories/steps/step-03-create-stories.md

@@ -8,7 +8,7 @@ outputFile: '{planning_artifacts}/epics.md'
 
 # Task References
 advancedElicitationTask: 'skill:bmad-advanced-elicitation'
-partyModeWorkflow: '{project-root}/_bmad/core/workflows/bmad-party-mode/workflow.md'
+partyModeWorkflow: 'skill:bmad-party-mode'
 ---
 
 # Step 3: Generate Epics and Stories

src/bmm/workflows/3-solutioning/bmad-create-epics-and-stories/steps/step-04-final-validation.md

@@ -4,10 +4,6 @@ description: 'Validate complete coverage of all requirements and ensure implemen
 
 # File References
 outputFile: '{planning_artifacts}/epics.md'
-
-# Task References
-advancedElicitationTask: 'skill:bmad-advanced-elicitation'
-partyModeWorkflow: '{project-root}/_bmad/core/workflows/bmad-party-mode/workflow.md'
 ---
 
 # Step 4: Final Validation