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/profile/__init__.py

@@ -0,0 +1,24 @@
+"""
+User Profile Management System for MarkiTect.
+
+This package provides comprehensive user profile management including:
+- CRUD operations for user profiles
+- Multiple profile support (personal, work, etc.)
+- JSON schema validation
+- Database integration with persistent storage
+- Profile inheritance and template support
+- Data export/import functionality
+"""
+
+from .manager import ProfileManager, ProfileNotFoundError, ProfileValidationError
+from .schema import ProfileSchema, ProfileData
+from .commands import profile_commands
+
+__all__ = [
+    'ProfileManager',
+    'ProfileSchema',
+    'ProfileData',
+    'ProfileNotFoundError',
+    'ProfileValidationError',
+    'profile_commands'
+]