feat: add configuration management

- Add Settings class using pydantic-settings
- Load config from environment variables with GM_ prefix
- Support encrypt_key and api_token (required, no defaults for security)
- Provide defaults for data_dir, host, port
- Add computed properties for db_path, ssh_keys_dir, repos_dir
- Add tests for config defaults and environment variable overrides
- Add Base class to app.models to unblock conftest.py imports

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/config.py

@@ -0,0 +1,43 @@
+import os
+from pathlib import Path
+from typing import Literal
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    """应用配置，从环境变量加载."""
+
+    # 安全配置
+    encrypt_key: str  # AES-256 密钥 (base64)
+    api_token: str    # API 认证 Token
+
+    # 路径配置
+    data_dir: Path = Path('./data')
+
+    # 服务器配置
+    host: str = '0.0.0.0'
+    port: int = 8000
+
+    model_config = SettingsConfigDict(
+        env_prefix='GM_',
+        env_file='.env',
+        env_file_encoding='utf-8',
+    )
+
+    @property
+    def db_path(self) -> Path:
+        """SQLite 数据库路径."""
+        return self.data_dir / 'git_manager.db'
+
+    @property
+    def ssh_keys_dir(self) -> Path:
+        """SSH 密钥存储目录."""
+        return self.data_dir / 'ssh_keys'
+
+    @property
+    def repos_dir(self) -> Path:
+        """仓库镜像存储目录."""
+        return self.data_dir / 'repos'
+
+
+settings = Settings()

backend/app/models/__init__.py

@@ -0,0 +1,11 @@
+"""ORM Models.
+
+NOTE: This module is a placeholder until Task 2.1.
+The Base class is needed by conftest.py for database fixtures.
+"""
+
+from sqlalchemy.orm import DeclarativeBase
+
+class Base(DeclarativeBase):
+    """Base class for all ORM models."""
+    pass

backend/tests/test_config.py

@@ -0,0 +1,32 @@
+import os
+import pytest
+import base64
+from pathlib import Path
+
+def test_config_defaults(test_env_vars, monkeypatch):
+    """测试配置默认值."""
+    # Clear GM_DATA_DIR to test default value
+    monkeypatch.delenv("GM_DATA_DIR", raising=False)
+
+    # Reload config to pick up the change
+    from app.config import Settings
+    settings = Settings()
+
+    assert settings.data_dir == Path('./data')
+    assert settings.host == '0.0.0.0'
+    assert settings.port == 8000
+
+def test_config_from_env(monkeypatch):
+    """测试从环境变量读取配置."""
+    # Set required security fields
+    monkeypatch.setenv("GM_ENCRYPT_KEY", base64.b64encode(b'test-key-32-bytes-long-1234567890').decode())
+    monkeypatch.setenv("GM_API_TOKEN", "test-token")
+    monkeypatch.setenv("GM_DATA_DIR", "/custom/data")
+    monkeypatch.setenv("GM_PORT", "9000")
+
+    # 重新加载配置
+    from app.config import Settings
+    settings = Settings()
+
+    assert settings.data_dir == Path('/custom/data')
+    assert settings.port == 9000