feat(config): implement configuration management for issue #7

- Create config.py with Config class
- Config precedence: ENV > config file > defaults
- data_dir: JIGAIDO_DATA_DIR env or ~/.jigaido/config.json or default
- bot_token: JIGAIDO_BOT_TOKEN env var
- ensure_data_dir() method to create data directory
- Add tests/test_config.py with 7 passing tests

Fixes #7

config.py

@@ -0,0 +1,37 @@
+"""JIGAIDO Configuration Management."""
+
+import json
+import os
+from pathlib import Path
+from typing import Optional
+
+DEFAULT_DATA_DIR = Path.home() / ".jigaido"
+
+
+class Config:
+    """JIGAIDO configuration with precedence: ENV > config file > defaults."""
+
+    def __init__(self):
+        self.data_dir: Path = self._resolve_data_dir()
+        self.bot_token: Optional[str] = os.environ.get("JIGAIDO_BOT_TOKEN")
+
+    def _resolve_data_dir(self) -> Path:
+        env_dir = os.environ.get("JIGAIDO_DATA_DIR")
+        if env_dir:
+            return Path(env_dir)
+
+        config_file = Path("~/.jigaido/config.json").expanduser()
+        if config_file.exists():
+            with open(config_file) as f:
+                config_data = json.load(f)
+                if "data_dir" in config_data:
+                    return Path(config_data["data_dir"])
+
+        return DEFAULT_DATA_DIR
+
+    def ensure_data_dir(self) -> None:
+        """Ensure the data directory exists."""
+        self.data_dir.mkdir(parents=True, exist_ok=True)
+
+
+config = Config()

tests/test_config.py

@@ -0,0 +1,76 @@
+"""Tests for config.py — configuration management."""
+
+import json
+import os
+import tempfile
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from config import Config, DEFAULT_DATA_DIR
+
+
+class TestConfigDataDir:
+    def test_default_data_dir(self, tmp_path):
+        """Test that default data_dir is ~/.jigaido when no config exists."""
+        with patch.dict(os.environ, {}, clear=True):
+            with patch("pathlib.Path.exists", return_value=False):
+                cfg = Config()
+                assert cfg.data_dir == DEFAULT_DATA_DIR
+
+    def test_env_override_data_dir(self, tmp_path):
+        """Test that JIGAIDO_DATA_DIR env var overrides config file."""
+        env_dir = "/custom/env/data/dir"
+        with patch.dict(os.environ, {"JIGAIDO_DATA_DIR": env_dir}, clear=False):
+            cfg = Config()
+            assert cfg.data_dir == Path(env_dir)
+
+    def test_config_file_data_dir(self, tmp_path):
+        """Test that config file is read when JIGAIDO_DATA_DIR not set."""
+        config_dir = tmp_path / ".jigaido"
+        config_dir.mkdir()
+        config_file = config_dir / "config.json"
+        config_file.write_text(json.dumps({"data_dir": "/custom/config/data"}))
+
+        with patch.dict(os.environ, {}, clear=True):
+            with patch("pathlib.Path.expanduser", return_value=config_file):
+                cfg = Config()
+                assert cfg.data_dir == Path("/custom/config/data")
+
+    def test_bot_token_from_env(self):
+        """Test that bot_token is read from JIGAIDO_BOT_TOKEN env var."""
+        with patch.dict(
+            os.environ, {"JIGAIDO_BOT_TOKEN": "test_token_123"}, clear=False
+        ):
+            cfg = Config()
+            assert cfg.bot_token == "test_token_123"
+
+    def test_bot_token_none_when_not_set(self):
+        """Test that bot_token is None when JIGAIDO_BOT_TOKEN not set."""
+        with patch.dict(os.environ, {}, clear=True):
+            cfg = Config()
+            assert cfg.bot_token is None
+
+
+class TestConfigEnsureDataDir:
+    def test_ensure_data_dir_creates_directory(self, tmp_path):
+        """Test that ensure_data_dir creates the directory if it doesn't exist."""
+        data_dir = tmp_path / "test_data_dir"
+        with patch.object(Config, "__init__", lambda self: None):
+            cfg = Config()
+            cfg.data_dir = data_dir
+            assert not data_dir.exists()
+            cfg.ensure_data_dir()
+            assert data_dir.exists()
+            assert data_dir.is_dir()
+
+    def test_ensure_data_dir_does_nothing_if_exists(self, tmp_path):
+        """Test that ensure_data_dir doesn't fail if directory already exists."""
+        data_dir = tmp_path / "existing_dir"
+        data_dir.mkdir()
+        with patch.object(Config, "__init__", lambda self: None):
+            cfg = Config()
+            cfg.data_dir = data_dir
+            cfg.ensure_data_dir()
+            assert data_dir.exists()