feat: implement comprehensive configuration management system with multi-mirror support

- Add ServerSettings class with pydantic-settings for type-safe configuration
- Support multiple PyPI mirror sources with priority-based fallback mechanism
- Implement RepositoryConfig and RepositoryManager for multi-repository support
- Add environment variable support for all configuration options
- Include private repository authentication configuration
- Add advanced dependency analysis settings (max depth, concurrency, security)
- Provide secure credential management with sensitive data masking
- Update documentation and configuration examples
- Add comprehensive test suite with 23 test cases covering all features
- Include demo script showcasing multi-mirror configuration capabilities

Configuration features:
- Primary, additional, and fallback index URLs
- Automatic duplicate URL removal with priority preservation
- Runtime configuration reloading
- Integration with repository manager for seamless multi-source queries

Signed-off-by: longhao <hal.long@outlook.com>

pypi_query_mcp/config/__init__.py

@@ -4,5 +4,32 @@ This package handles configuration loading, validation, and management
 for the MCP server, including private registry settings.
 """
 
-# Configuration exports will be added as modules are implemented
-__all__ = []
+from .repository import (
+    AuthType,
+    RepositoryConfig,
+    RepositoryManager,
+    RepositoryType,
+    get_repository_manager,
+    reload_repository_manager,
+)
+from .settings import (
+    ServerSettings,
+    get_settings,
+    reload_settings,
+    update_settings,
+)
+
+__all__ = [
+    # Settings
+    "ServerSettings",
+    "get_settings",
+    "reload_settings",
+    "update_settings",
+    # Repository
+    "RepositoryConfig",
+    "RepositoryManager",
+    "RepositoryType",
+    "AuthType",
+    "get_repository_manager",
+    "reload_repository_manager",
+]