feat: Extract BMGD module and implement workflow vendoring

This commit extracts game development functionality from BMM into a standalone
BMGD (BMad Game Development) module and implements workflow vendoring to enable
module independence.

BMGD Module Creation:
- Moved agents: game-designer, game-dev, game-architect from BMM to BMGD
- Moved team config: team-gamedev
- Created new Game Dev Scrum Master agent using workflow vendoring pattern
- Reorganized workflows into industry-standard game dev phases:
  * Phase 1 (Preproduction): brainstorm-game, game-brief
  * Phase 2 (Design): gdd, narrative
  * Phase 3 (Technical): game-architecture
  * Phase 4 (Production): vendored from BMM workflows
- Updated all module metadata and config_source references

Workflow Vendoring Feature:
- Enables modules to copy workflows from other modules during installation
- Build-time process that updates config_source in vendored workflows
- New agent YAML attribute: workflow-install (build-time metadata)
- Final compiled agents use workflow-install value for workflow attribute
- Implementation in module manager: vendorCrossModuleWorkflows()
- Allows standalone module installation without forced dependencies

Technical Changes:
- tools/cli/lib/yaml-xml-builder.js: Use workflow-install for workflow attribute
- tools/cli/installers/lib/modules/manager.js: Add vendoring functions
- tools/schema/agent.js: Add workflow-install to menu item schema
- Updated 3 documentation files with workflow vendoring details

BMM Workflow Updates:
- workflow-status/init: Added game detection checkpoint
- workflow-status/paths/game-design.yaml: Redirect to BMGD module
- prd/instructions.md: Route game projects to BMGD
- research/instructions-market.md: Reference BMGD for game development

Documentation:
- Created comprehensive BMGD module README
- Added workflow vendoring documentation
- Updated BMB agent creation and module creation guides

tools/cli/lib/yaml-xml-builder.js

@@ -311,7 +311,15 @@ class YamlXmlBuilder {
         const attrs = [`cmd="${trigger}"`];
 
         // Add handler attributes
-        if (item.workflow) attrs.push(`workflow="${item.workflow}"`);
+        // If workflow-install exists, use its value for workflow attribute (vendoring)
+        // workflow-install is build-time metadata - tells installer where to copy workflows
+        // The final XML should only have workflow pointing to the install location
+        if (item['workflow-install']) {
+          attrs.push(`workflow="${item['workflow-install']}"`);
+        } else if (item.workflow) {
+          attrs.push(`workflow="${item.workflow}"`);
+        }
+
         if (item['validate-workflow']) attrs.push(`validate-workflow="${item['validate-workflow']}"`);
         if (item.exec) attrs.push(`exec="${item.exec}"`);
         if (item.tmpl) attrs.push(`tmpl="${item.tmpl}"`);