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

src/modules/bmb/workflows/create-module/module-structure.md

@@ -136,6 +136,40 @@ Tasks should be used for:
 - Declare dependencies in config.yaml
 - Version compatibility notes
 
+### Workflow Vendoring (Advanced)
+
+For modules that need workflows from other modules but want to remain standalone, use **workflow vendoring**:
+
+**In Agent YAML:**
+
+```yaml
+menu:
+  - trigger: command-name
+    workflow: '{project-root}/bmad/SOURCE_MODULE/workflows/path/workflow.yaml'
+    workflow-install: '{project-root}/bmad/THIS_MODULE/workflows/vendored/workflow.yaml'
+    description: 'Command description'
+```
+
+**What Happens:**
+
+- During installation, workflows are copied from `workflow` to `workflow-install` location
+- Vendored workflows get `config_source` updated to reference this module's config
+- Compiled agent only references the `workflow-install` path
+- Module becomes fully standalone - no source module dependency required
+
+**Use Cases:**
+
+- Specialized modules that reuse common workflows with different configs
+- Domain-specific adaptations (e.g., game dev using standard dev workflows)
+- Testing workflows in isolation
+
+**Benefits:**
+
+- Module independence (no forced dependencies)
+- Clean namespace (workflows in your module)
+- Config isolation (use your module's settings)
+- Customization ready (modify vendored workflows freely)
+
 ## Installation Infrastructure
 
 ### Required: \_module-installer/install-config.yaml