feat: implement comprehensive capability inclusion management system

Added systematic approach to manage capability inclusion via subrepos and prevent code duplication. This addresses the architectural challenge of ensuring Claude recognizes, uses, and respects included capabilities.

New Capability Management System:
- CAPABILITY_REGISTRY.md: Complete registry of all included capabilities
- CLAUDE_CAPABILITY_REFERENCE.md: Quick lookup guide for Claude to prevent duplication
- tools/capability_discovery.py: Automated discovery and validation tool
- Makefile targets: capability-report, capability-search, capability-validate

Registry Coverage:
- Submodule capabilities: issue-facade (universal issue tracking), wiki (documentation)
- Local capabilities: markitect-content (content parsing), markitect-utils (utilities)
- External dependencies: Click, pytest, SQLAlchemy, requests

Agent Integration:
- Updated project-management and tdd-workflow agents with capability awareness
- Clear guidelines for checking existing functionality before implementing
- Integration patterns for using capabilities properly

Discovery & Validation:
- Automated capability discovery across submodules and local directories
- Search functionality to find existing implementations
- Validation tools to detect potential code duplication
- Claude-readable interfaces and usage patterns

Benefits:
- Prevents accidental functionality duplication
- Ensures proper separation of concerns
- Provides easy capability extension and bugfixing
- Maintains clean interfaces between core and capabilities
- Guides Claude to use existing capabilities efficiently

Usage:
- make capability-report: Generate complete capability overview
- make capability-search TERM=xyz: Find existing implementations
- make capability-validate FILE=path: Check for proper capability usage

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

agents/agent-tdd-workflow.md

@@ -104,6 +104,11 @@ You are the authoritative guide for the TDD8 workflow using the issue-facade sys
 - `cd issue-facade && python -m cli.main create "Title" "Description"` - Create new issue
 - `cd issue-facade && python -m cli.main close ISSUE_NUM` - Close completed issue
 
+**Capability Awareness:**
+- **Before implementing**: Check `CAPABILITY_REGISTRY.md` for existing functionality
+- **Use existing capabilities**: Never reimplement issue management, content parsing, or utilities
+- **Capability discovery**: Use `make capability-search TERM=function_name` to find existing implementations
+
 **Supporting Commands:**
 - `make test-coverage` - Analyze test coverage
 - `make test` - Run all tests