feat: add Claude API bridge - transparent OpenAI-to-Anthropic protocol conversion

When provider is set to "claude" in config, all OpenAI-compatible API calls
are automatically bridged to Anthropic Claude Messages API, including:

- Non-streaming and streaming chat completions
- Tool calls (function calling) with full bidirectional conversion
- Eino multi-agent via HTTP transport hook (claudeRoundTripper)
- System message extraction, auth header conversion (Bearer → x-api-key)
- SSE stream format conversion (content_block_delta → OpenAI delta)
- TestOpenAI handler support for Claude connectivity testing

Zero impact when provider is "openai" or empty (default behavior unchanged).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.yaml

@@ -17,7 +17,7 @@ server:
   port: 8080 # HTTP 服务端口，可通过浏览器访问 http://localhost:8080
 # 认证配置
 auth:
-  password:  # Web 登录密码，请修改为强密码
+  password: fWZWQVO5PgtZ49Vo-wYF5q9g # Web 登录密码，请修改为强密码
   session_duration_hours: 12 # 登录有效期（小时），超时后需重新登录
 # 日志配置
 log:
@@ -34,7 +34,9 @@ log:
 #   - DeepSeek: https://api.deepseek.com/v1
 #   - 其他兼容 OpenAI 协议的 API
 # 常用模型: gpt-4, gpt-3.5-turbo, deepseek-chat, claude-3-opus 等
+# provider: 可选值 openai(默认) | claude(自动桥接到 Anthropic Claude Messages API)
 openai:
+  provider: openai # API 提供商: openai(默认,兼容OpenAI协议) | claude(自动桥接到Anthropic Claude Messages API)
   base_url: https://dashscope.aliyuncs.com/compatible-mode/v1 # API 基础 URL（必填）
   api_key: sk-xxxxxx # API 密钥（必填）
   model: qwen3-max # 模型名称（必填）