docs: add anthropic-messages protocol examples to README and config

Add configuration examples and documentation for the new
anthropic-messages protocol:

- config.example.json: Add claude-opus-4.6 example with anthropic-messages
- README.md: Add "Anthropic Messages API (native format)" section
- README.zh.md: Add Chinese version of the documentation

This helps users understand when to use anthropic-messages vs
anthropic protocol and fixes issue #269.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -1097,6 +1097,24 @@ This design also enables **multi-agent support** with flexible provider selectio
 
 > Run `picoclaw auth login --provider anthropic` to paste your API token.
 
+**Anthropic Messages API (native format)**
+
+For direct Anthropic API access or custom endpoints that only support Anthropic's native message format:
+
+```json
+{
+  "model_name": "claude-opus-4-6",
+  "model": "anthropic-messages/claude-opus-4-6",
+  "api_key": "sk-ant-your-key",
+  "api_base": "https://api.anthropic.com"
+}
+```
+
+> Use `anthropic-messages` protocol when:
+> - Connecting directly to Anthropic's API (fixes 404 errors with `/v1/messages` endpoint)
+> - Using custom endpoints that only support Anthropic's native format
+> - Avoiding OpenAI-compatible wrapper layers
+
 **Ollama (local)**
 
 ```json

README.zh.md

@@ -593,6 +593,24 @@ Agent 读取 HEARTBEAT.md
 
 > 运行 `picoclaw auth login --provider anthropic` 来设置 OAuth 凭证。
 
+**Anthropic Messages API（原生格式）**
+
+用于直接访问 Anthropic API 或仅支持 Anthropic 原生消息格式的自定义端点：
+
+```json
+{
+  "model_name": "claude-opus-4-6",
+  "model": "anthropic-messages/claude-opus-4-6",
+  "api_key": "sk-ant-your-key",
+  "api_base": "https://api.anthropic.com"
+}
+```
+
+> 使用 `anthropic-messages` 协议的场景：
+> - 直接连接 Anthropic API（修复 `/v1/messages` 端点的 404 错误）
+> - 使用仅支持 Anthropic 原生格式的自定义端点
+> - 避免 OpenAI 兼容包装层
+
 **Ollama (本地)**
 
 ```json

config/config.example.json

@@ -25,6 +25,13 @@
       "api_base": "https://api.anthropic.com/v1",
       "thinking_level": "high"
     },
+    {
+      "_comment": "Anthropic Messages API - use native format for direct Anthropic API access",
+      "model_name": "claude-opus-4-6",
+      "model": "anthropic-messages/claude-opus-4-6",
+      "api_key": "sk-ant-your-key",
+      "api_base": "https://api.anthropic.com"
+    },
     {
       "model_name": "gemini",
       "model": "antigravity/gemini-2.0-flash",