refactor: add Settings singleton pattern for config management

AGENTS.md

@@ -8,11 +8,14 @@ TrytonMCP is an MCP (Model Context Protocol) server that enables LLMs to interac
 
 ```
 TrytonMCP/
-├── src/tryton-mcp/
-│   ├── __init__.py
-│   └── server.py          # Main MCP server with tool definitions
-├── test_rpc.py            # Standalone RPC test script
-└── pyproject.toml         # Project dependencies
+├── src/
+│   └── tryton_mcp/
+│       ├── __init__.py
+│       ├── config.py          # Settings singleton with TrytonSettings
+│       └── server.py          # Main MCP server with tool definitions
+├── test_rpc.py                 # Standalone RPC test script
+├── pyproject.toml             # Project dependencies
+└── .env.example               # Environment variables template
 ```
 
 ## Architecture
@@ -23,16 +26,15 @@ TrytonMCP/
 
 ### Core Components
 
-1. **Client Connection** (`server.py:45-47, 59-61, 73-75`)
-   - Creates a new `Client` instance for each tool call
-   - Credentials are hardcoded in `TRYTON_CREDENTIALS` dict
+1. **Settings** (`config.py`) - Singleton pattern for configuration management
+   - Uses environment variables with defaults
+   - Provides `to_dict()` and `get_client()` methods
+   - Validates required fields in `__post_init__`
 
-2. **Tools** - Functions decorated with `@mcp.tool()`:
-   - `create_schedule` (line 32-54) - Creates appointments in Naliia module
-   - `find_service_centers` (line 57-69) - Searches service centers
-   - `find_products_and_services` (line 71-83) - Searches salable products
-
-3. **Context** (`server.py:20-24`) - Dataclass for managing client state (currently unused)
+2. **Tools** (`server.py`) - Functions decorated with `@mcp.tool()`:
+   - `create_schedule` - Creates appointments in Naliia module
+   - `find_service_centers` - Searches service centers
+   - `find_products_and_services` - Searches salable products
 
 ## Adding New Tools
 
@@ -41,7 +43,7 @@ To add a new Tryton model as an MCP tool:
 ```python
 @mcp.tool()
 def your_tool_name(param1: int, param2: str) -> List[dict]:
-    client = Client(**TRYTON_CREDENTIALS)
+    client = settings.get_client()
     client.connect()
     
     name = "model.your.model.method"