refactor: Modularize MCP server with command batching

- Split monolithic mcp/server.py (1874 lines) into haproxy_mcp/ package:
  - config.py: Configuration constants and environment variables
  - exceptions.py: Custom exception classes
  - validation.py: Input validation functions
  - haproxy_client.py: HAProxy Runtime API client with batch support
  - file_ops.py: Atomic file operations with locking
  - utils.py: CSV parsing utilities
  - tools/: MCP tools organized by function
    - domains.py: Domain management (3 tools)
    - servers.py: Server management (7 tools)
    - health.py: Health checks (3 tools)
    - monitoring.py: Monitoring (4 tools)
    - configuration.py: Config management (4 tools)

- Add haproxy_cmd_batch() for sending multiple commands in single TCP connection
- Optimize server operations: 1 connection instead of 2 per server
- Optimize startup restore: All servers in 1 connection (was 2×N)
- Update type hints to Python 3.9+ style (built-in generics)
- Remove unused imports and functions
- Update CLAUDE.md with new structure and performance notes

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -319,6 +319,12 @@ api.example.com → pool_6
 - **Input validation**: Domain format, IP (v4/v6), port range, slot limits
 - **Bulk limits**: Max 10 servers per bulk add, 10KB JSON size limit
 
+### Performance Optimization
+- **Command batching**: Multiple HAProxy commands sent in single TCP connection
+  - Server config (addr + state): 1 connection instead of 2
+  - Startup restore: All servers restored in 1 connection (was 2×N for N servers)
+  - Example: 7 servers restored = 1 connection (was 14 connections)
+
 ## HAProxy Runtime API
 
 ```bash
@@ -345,8 +351,20 @@ echo "set server pool_1/pool_1_1 state ready" | nc localhost 9999
 
 ```
 /opt/haproxy/
-├── mcp/                 # MCP server (streamable-http)
-│   └── server.py        # Main MCP server (~1700 lines, 22 tools)
+├── haproxy_mcp/         # MCP server package (streamable-http)
+│   ├── server.py        # Main entry point
+│   ├── config.py        # Configuration and constants
+│   ├── exceptions.py    # Exception classes
+│   ├── validation.py    # Input validation
+│   ├── haproxy_client.py # HAProxy Runtime API client
+│   ├── file_ops.py      # File I/O operations
+│   ├── utils.py         # Parsing utilities
+│   └── tools/           # MCP tools (22 total)
+│       ├── domains.py   # Domain management (3 tools)
+│       ├── servers.py   # Server management (7 tools)
+│       ├── health.py    # Health checks (3 tools)
+│       ├── monitoring.py # Monitoring (4 tools)
+│       └── configuration.py # Config management (4 tools)
 ├── conf/
 │   ├── haproxy.cfg      # Main HAProxy config (100 pool backends)
 │   ├── domains.map      # Domain → Pool mapping