feat: implement comprehensive User Profile Management System (issue #107)

Complete user profile management system with CRUD operations and CLI integration:

## 🎯 Core Features Delivered
- **ProfileManager**: Complete CRUD operations with database integration
- **JSON Schema validation**: Comprehensive profile data validation
- **Multiple profile support**: Named profiles (personal, work, etc.)
- **Default profile system**: Set and manage default profiles
- **Profile inheritance**: Merge profiles with override capabilities
- **Template integration**: Extract flattened variables for template filling

## 📋 Profile Schema & Data Model
- **Structured data classes**: ProfileData, ContactInfo, Address, Organization
- **JSON Schema validation**: Full validation with field descriptions
- **Flexible structure**: Support for nested data and custom fields
- **Timestamp management**: Automatic created_at/updated_at tracking

## 🖥️ CLI Integration Complete
- **9 CLI Commands**: create, show, list, update, delete, set-default, export, import, variables
- **Multiple formats**: JSON, YAML, and table output formats
- **Interactive mode**: Guided profile creation and updates
- **Export/Import**: Full profile portability with validation
- **Template variables**: Extract flattened variables for template systems

## 📊 Implementation Stats
- **ProfileManager**: 500+ lines with comprehensive functionality
- **ProfileSchema**: 350+ lines with validation and data structures
- **CLI Commands**: 450+ lines of professional command interface
- **Test Coverage**: 66 tests (36 core + 30 CLI) with 100% pass rate

## 🚀 **Ready for Template Integration**
Foundation complete for Issue #99 (Auto Fill Templates) with:
- Template variable extraction from profiles
- Default profile system for seamless integration
- Profile merging for complex template scenarios
- Professional CLI for user profile management

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

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

markitect/cli.py

@@ -38,6 +38,13 @@ try:
 except ImportError:
     COST_TRACKING_AVAILABLE = False
 
+# Import profile management commands
+try:
+    from .profile.commands import profile_commands
+    PROFILE_MANAGEMENT_AVAILABLE = True
+except ImportError:
+    PROFILE_MANAGEMENT_AVAILABLE = False
+
 
 def get_database_path(config):
     """Get database path from config."""
@@ -6556,6 +6563,10 @@ def categories(config):
 if COST_TRACKING_AVAILABLE:
     cli.add_command(cost_commands)
 
+# Register profile management commands
+if PROFILE_MANAGEMENT_AVAILABLE:
+    cli.add_command(profile_commands)
+
 # Register paradigms commands
 cli.add_command(paradigms)