feat: implement host strategy classes with inheritance architecture

Add concrete host strategy implementations using decorator registration
with inheritance patterns for code reuse and maintainability.

Strategy families:
- Claude family: ClaudeDesktopHostStrategy, ClaudeCodeHostStrategy
  * Shared validation requiring absolute command paths
  * Common Anthropic-specific configuration handling
- Cursor family: CursorHostStrategy, LMStudioHostStrategy
  * Flexible path handling and shared configuration format
  * Common cursor-based editor patterns
- Independent: VSCodeHostStrategy, GeminiHostStrategy
  * Unique configuration formats and validation rules
  * Updated Gemini strategy based on official documentation

Features:
- @register_host_strategy decorator usage for all strategies
- Inheritance-based code sharing within families
- Host-specific configuration path resolution
- Atomic configuration operations with backup integration
- Consolidated MCPServerConfig model usage throughout

Updates Gemini strategy to use official ~/.gemini/settings.json
configuration path and mcpServers key structure.

Author: LittleCoinCoin