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>

web/static/js/settings.js

@@ -102,6 +102,10 @@ async function loadConfig(loadTools = true) {
         currentConfig = await response.json();
         
         // 填充OpenAI配置
+        const providerEl = document.getElementById('openai-provider');
+        if (providerEl) {
+            providerEl.value = currentConfig.openai.provider || 'openai';
+        }
         document.getElementById('openai-api-key').value = currentConfig.openai.api_key || '';
         document.getElementById('openai-base-url').value = currentConfig.openai.base_url || '';
         document.getElementById('openai-model').value = currentConfig.openai.model || '';
@@ -753,6 +757,7 @@ async function applySettings() {
         });
         
         // 验证必填字段
+        const provider = document.getElementById('openai-provider')?.value || 'openai';
         const apiKey = document.getElementById('openai-api-key').value.trim();
         const baseUrl = document.getElementById('openai-base-url').value.trim();
         const model = document.getElementById('openai-model').value.trim();
@@ -821,6 +826,7 @@ async function applySettings() {
         const wecomAgentIdVal = document.getElementById('robot-wecom-agent-id')?.value.trim();
         const config = {
             openai: {
+                provider: provider,
                 api_key: apiKey,
                 base_url: baseUrl,
                 model: model
@@ -981,6 +987,7 @@ async function testOpenAIConnection() {
     const btn = document.getElementById('test-openai-btn');
     const resultEl = document.getElementById('test-openai-result');
 
+    const provider = document.getElementById('openai-provider')?.value || 'openai';
     const baseUrl = document.getElementById('openai-base-url').value.trim();
     const apiKey = document.getElementById('openai-api-key').value.trim();
     const model = document.getElementById('openai-model').value.trim();
@@ -1001,6 +1008,7 @@ async function testOpenAIConnection() {
             method: 'POST',
             headers: { 'Content-Type': 'application/json' },
             body: JSON.stringify({
+                provider: provider,
                 base_url: baseUrl,
                 api_key: apiKey,
                 model: model

web/templates/index.html

@@ -1365,6 +1365,13 @@
                                 <div class="settings-subsection">
                                     <h4 data-i18n="settingsBasic.openaiConfig">OpenAI 配置</h4>
                                     <div class="settings-form">
+                                        <div class="form-group">
+                                            <label for="openai-provider">API 提供商</label>
+                                            <select id="openai-provider" style="width: 100%; padding: 0.5rem 0.75rem; border: 1px solid var(--border-color, #e2e8f0); border-radius: 6px; background: var(--card-bg, #fff); color: var(--text-color, #2d3748); font-size: 0.875rem;">
+                                                <option value="openai">OpenAI / 兼容 OpenAI 协议</option>
+                                                <option value="claude">Claude (Anthropic Messages API)</option>
+                                            </select>
+                                        </div>
                                         <div class="form-group">
                                             <label for="openai-base-url">Base URL <span style="color: red;">*</span></label>
                                             <input type="text" id="openai-base-url" data-i18n="settingsBasic.openaiBaseUrlPlaceholder" data-i18n-attr="placeholder" placeholder="https://api.openai.com/v1" required />