Implement configuration loader module

This commit implements a robust configuration loader using Pydantic Settings that handles:

Features:
- Environment variable loading with .env file support
- Type validation and field constraints
- Gitea configuration (URL, token, owner, repo)
- HTTP server configuration (host, port)
- Optional HTTP authentication token
- Optional tool filtering (enabled/disabled tool lists)

Implementation:
- GiteaSettings class with Pydantic validation
- URL validation ensuring http:// or https:// prefix
- Helper properties for parsing comma-separated tool lists
- get_gitea_mcp_env() method to pass config to wrapped MCP server
- load_settings() factory function with optional env_file path

Documentation:
- .env.example template with all configuration options
- Comprehensive docstrings and type hints

This module unblocks both the tool filtering (#12) and HTTP authentication middleware (#13) implementations.

Closes #11

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/gitea_http_wrapper/config/__init__.py

@@ -1,3 +1,5 @@
 """Configuration loader module."""
 
-__all__ = []
+from .settings import GiteaSettings, load_settings
+
+__all__ = ["GiteaSettings", "load_settings"]