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/bmgd/teams/team-gamedev.yaml

@@ -0,0 +1,16 @@
+# <!-- Powered by BMAD-CORE™ -->
+bundle:
+  name: Team Game Development
+  icon: 🎮
+  description: Specialized game development team including Game Designer (creative vision and GDD), Game Developer (implementation and code), Game Architect (technical systems and infrastructure), and Game Dev Scrum Master (sprint coordination). Perfect for game projects across all scales and platforms.
+agents:
+  - game-designer
+  - game-dev
+  - game-architect
+  - game-scrum-master
+
+workflows:
+  - brainstorm-game
+  - game-brief
+  - gdd
+  - narrative