feat(02-01): create bot configuration module

- BotConfig dataclass with from_env() classmethod
- Loads BOT_TOKEN (required), ALLOWED_USERS, DATABASE_URL, LOG_LEVEL
- Raises ValueError if BOT_TOKEN is missing

src/moai/bot/config.py

@@ -0,0 +1,64 @@
+"""Bot configuration loaded from environment variables.
+
+Provides BotConfig dataclass with configuration loaded from environment.
+Required variables will raise ValueError if missing.
+"""
+
+import os
+from dataclasses import dataclass
+
+
+@dataclass
+class BotConfig:
+    """Configuration for the MoAI Telegram bot.
+
+    Attributes:
+        bot_token: Telegram Bot API token (required).
+        allowed_users: Set of allowed Telegram user IDs. Empty means all users allowed.
+        database_url: SQLAlchemy database URL.
+        log_level: Logging level string (DEBUG, INFO, WARNING, ERROR).
+    """
+
+    bot_token: str
+    allowed_users: set[int]
+    database_url: str
+    log_level: str
+
+    @classmethod
+    def from_env(cls) -> "BotConfig":
+        """Load configuration from environment variables.
+
+        Environment variables:
+            BOT_TOKEN (required): Telegram bot token from @BotFather.
+            ALLOWED_USERS (optional): Comma-separated Telegram user IDs.
+            DATABASE_URL (optional): Database URL, defaults to SQLite.
+            LOG_LEVEL (optional): Logging level, defaults to INFO.
+
+        Returns:
+            BotConfig instance populated from environment.
+
+        Raises:
+            ValueError: If BOT_TOKEN is not set.
+        """
+        bot_token = os.environ.get("BOT_TOKEN")
+        if not bot_token:
+            raise ValueError("BOT_TOKEN environment variable is required")
+
+        # Parse allowed users from comma-separated string
+        allowed_users_str = os.environ.get("ALLOWED_USERS", "")
+        allowed_users: set[int] = set()
+        if allowed_users_str.strip():
+            for user_id in allowed_users_str.split(","):
+                user_id = user_id.strip()
+                if user_id:
+                    allowed_users.add(int(user_id))
+
+        database_url = os.environ.get("DATABASE_URL", "sqlite+aiosqlite:///./moai.db")
+        log_level = os.environ.get("LOG_LEVEL", "INFO")
+
+        return cls(
+            bot_token=bot_token,
+            allowed_users=allowed_users,
+            database_url=database_url,
+            log_level=log_level,
+        )