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

docs/installers-bundlers/installers-modules-platforms-reference.md

@@ -311,6 +311,66 @@ bmad status -v      # Detailed status
 - Agent references (cross-module)
 - Template dependencies
 - Partial module installation (only required files)
+- Workflow vendoring for standalone module operation
+
+## Workflow Vendoring
+
+**Problem**: Modules that reference workflows from other modules create dependencies, forcing users to install multiple modules even when they only need one.
+
+**Solution**: Workflow vendoring allows modules to copy workflows from other modules during installation, making them fully standalone.
+
+### How It Works
+
+Agents can specify both `workflow` (source location) and `workflow-install` (destination location) in their menu items:
+
+```yaml
+menu:
+  - trigger: create-story
+    workflow: '{project-root}/bmad/bmm/workflows/4-implementation/create-story/workflow.yaml'
+    workflow-install: '{project-root}/bmad/bmgd/workflows/4-production/create-story/workflow.yaml'
+    description: 'Create a game feature story'
+```
+
+**During Installation:**
+
+1. **Vendoring Phase**: Before copying module files, the installer:
+   - Scans source agent YAML files for `workflow-install` attributes
+   - Copies entire workflow folders from `workflow` path to `workflow-install` path
+   - Updates vendored `workflow.yaml` files to reference target module's config
+
+2. **Compilation Phase**: When compiling agents:
+   - If `workflow-install` exists, uses its value for the `workflow` attribute
+   - `workflow-install` is build-time metadata only, never appears in final XML
+   - Compiled agent references vendored workflow location
+
+3. **Config Update**: Vendored workflows get their `config_source` updated:
+
+   ```yaml
+   # Source workflow (in bmm):
+   config_source: "{project-root}/bmad/bmm/config.yaml"
+
+   # Vendored workflow (in bmgd):
+   config_source: "{project-root}/bmad/bmgd/config.yaml"
+   ```
+
+**Result**: Modules become completely standalone with their own copies of needed workflows, configured for their specific use case.
+
+### Example Use Case: BMGD Module
+
+The BMad Game Development module vendors implementation workflows from BMM:
+
+- Game Dev Scrum Master agent references BMM workflows
+- During installation, workflows are copied to `bmgd/workflows/4-production/`
+- Vendored workflows use BMGD's config (with game-specific settings)
+- BMGD can be installed without BMM dependency
+
+### Benefits
+
+✅ **Module Independence** - No forced dependencies
+✅ **Clean Namespace** - Workflows live in their module
+✅ **Config Isolation** - Each module uses its own configuration
+✅ **Customization Ready** - Vendored workflows can be modified independently
+✅ **No User Confusion** - Avoid partial module installations
 
 ### File Processing
 
@@ -318,6 +378,7 @@ bmad status -v      # Detailed status
 - Excludes `_module-installer/` directories
 - Replaces path placeholders at runtime
 - Injects activation blocks
+- Vendors cross-module workflows (see Workflow Vendoring below)
 
 ### Web Bundling