refactor: Extract large functions, improve exception handling, remove duplicates

## Large function extraction
- servers.py: Extract 8 _impl functions from register_server_tools (449 lines)
- certificates.py: Extract 7 _impl functions from register_certificate_tools (386 lines)
- MCP tool wrappers now delegate to module-level implementation functions

## Exception handling improvements
- Replace 11 broad `except Exception` with specific types
- health.py: (OSError, subprocess.SubprocessError)
- configuration.py: (HaproxyError, IOError, OSError, ValueError)
- servers.py: (IOError, OSError, ValueError)
- certificates.py: FileNotFoundError, (subprocess.SubprocessError, OSError)

## Duplicate code extraction
- Add parse_servers_state() to utils.py (replaces 4 duplicate parsers)
- Add disable_server_slot() to utils.py (replaces duplicate patterns)
- Update health.py, servers.py, domains.py to use new helpers

## Other improvements
- Add TypedDict types in file_ops.py and health.py
- Set file permissions (0o600) for sensitive files
- Update tests to use specific exception types

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

haproxy_mcp/utils.py

@@ -1,7 +1,58 @@
 """Utility functions for HAProxy MCP Server."""
 
 from typing import Dict, Generator
-from .config import StatField
+from .config import StatField, StateField, STATE_MIN_COLUMNS
+from .haproxy_client import haproxy_cmd_batch
+
+
+def parse_servers_state(state_output: str) -> dict[str, dict[str, dict[str, str]]]:
+    """Parse 'show servers state' output.
+
+    Args:
+        state_output: Raw output from HAProxy 'show servers state' command
+
+    Returns:
+        Nested dict: {backend: {server: {addr: str, port: str, state: str}}}
+
+    Example:
+        state = haproxy_cmd("show servers state")
+        parsed = parse_servers_state(state)
+        # parsed["pool_1"]["pool_1_1"] == {"addr": "10.0.0.1", "port": "8080", "state": "2"}
+    """
+    result: dict[str, dict[str, dict[str, str]]] = {}
+    for line in state_output.split("\n"):
+        parts = line.split()
+        if len(parts) >= STATE_MIN_COLUMNS:
+            backend = parts[StateField.BE_NAME]
+            server = parts[StateField.SRV_NAME]
+            addr = parts[StateField.SRV_ADDR]
+            port = parts[StateField.SRV_PORT]
+            state = parts[StateField.SRV_OP_STATE] if len(parts) > StateField.SRV_OP_STATE else ""
+
+            if backend not in result:
+                result[backend] = {}
+            result[backend][server] = {
+                "addr": addr,
+                "port": port,
+                "state": state,
+            }
+    return result
+
+
+def disable_server_slot(backend: str, server: str) -> None:
+    """Disable a server slot (set to maint and clear address).
+
+    Args:
+        backend: Backend name (e.g., 'pool_1')
+        server: Server name (e.g., 'pool_1_1')
+
+    Raises:
+        HaproxyError: If HAProxy command fails
+    """
+    haproxy_cmd_batch([
+        f"set server {backend}/{server} state maint",
+        f"set server {backend}/{server} addr 0.0.0.0 port 0"
+    ])
 
 
 def parse_stat_csv(stat_output: str) -> Generator[Dict[str, str], None, None]: