feat(proxy): implement provider adapter pattern with OpenRouter support

This major refactoring introduces a modular provider adapter architecture
to support format transformation between different AI API formats.

New features:
- Add ProviderAdapter trait for unified provider abstraction
- Implement Claude, Codex, and Gemini adapters with specific logic
- Add Anthropic ↔ OpenAI format transformation for OpenRouter compatibility
- Support model mapping from provider configuration (ANTHROPIC_MODEL, etc.)
- Add OpenRouter preset to Claude provider presets

Refactoring:
- Extract authentication logic into auth.rs with AuthInfo and AuthStrategy
- Move URL building and request transformation to individual adapters
- Simplify ProviderRouter to only use proxy target providers
- Refactor RequestForwarder to use adapter-based request/response handling
- Use whitelist mode for header forwarding (only pass necessary headers)

Architecture:
- providers/adapter.rs: ProviderAdapter trait definition
- providers/auth.rs: AuthInfo, AuthStrategy types
- providers/claude.rs: Claude adapter with OpenRouter detection
- providers/codex.rs: Codex (OpenAI) adapter
- providers/gemini.rs: Gemini (Google) adapter
- providers/models/: Anthropic and OpenAI API data models
- providers/transform.rs: Bidirectional format transformation

src-tauri/src/proxy/providers/models/openai.rs

@@ -0,0 +1,113 @@
+//! OpenAI API 数据模型
+//!
+//! 用于 OpenAI Chat Completions API 的请求/响应格式转换
+
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+
+/// OpenAI 请求
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIRequest {
+    pub model: String,
+    pub messages: Vec<OpenAIMessage>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub max_tokens: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub temperature: Option<f32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub stream: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tools: Option<Vec<OpenAITool>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tool_choice: Option<Value>,
+}
+
+/// OpenAI 消息
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIMessage {
+    pub role: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub content: Option<Value>, // String 或 Vec<ContentPart>
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tool_calls: Option<Vec<OpenAIToolCall>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tool_call_id: Option<String>,
+}
+
+/// OpenAI 内容部分
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum OpenAIContentPart {
+    #[serde(rename = "text")]
+    Text { text: String },
+    #[serde(rename = "image_url")]
+    ImageUrl { image_url: ImageUrl },
+}
+
+/// 图片 URL
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ImageUrl {
+    pub url: String,
+}
+
+/// OpenAI 工具调用
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIToolCall {
+    pub id: String,
+    #[serde(rename = "type")]
+    pub call_type: String,
+    pub function: OpenAIFunction,
+}
+
+/// OpenAI 函数
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIFunction {
+    pub name: String,
+    pub arguments: String, // JSON 字符串
+}
+
+/// OpenAI 工具定义
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAITool {
+    #[serde(rename = "type")]
+    pub tool_type: String,
+    pub function: OpenAIFunctionDef,
+}
+
+/// OpenAI 函数定义
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIFunctionDef {
+    pub name: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub description: Option<String>,
+    pub parameters: Value,
+}
+
+/// OpenAI 响应
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIResponse {
+    pub id: String,
+    pub object: String,
+    pub created: u64,
+    pub model: String,
+    pub choices: Vec<OpenAIChoice>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub usage: Option<OpenAIUsage>,
+}
+
+/// OpenAI 选择
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIChoice {
+    pub index: u32,
+    pub message: OpenAIMessage,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub finish_reason: Option<String>,
+}
+
+/// OpenAI 使用量
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OpenAIUsage {
+    pub prompt_tokens: u32,
+    pub completion_tokens: u32,
+    pub total_tokens: u32,
+}