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/auth.rs

@@ -0,0 +1,92 @@
+//! Authentication Types
+//!
+//! 定义认证信息和认证策略，支持多种上游供应商的认证方式。
+
+/// 认证信息
+///
+/// 包含 API Key 和对应的认证策略
+#[derive(Debug, Clone)]
+pub struct AuthInfo {
+    /// API Key
+    pub api_key: String,
+    /// 认证策略
+    pub strategy: AuthStrategy,
+}
+
+impl AuthInfo {
+    /// 创建新的认证信息
+    pub fn new(api_key: String, strategy: AuthStrategy) -> Self {
+        Self { api_key, strategy }
+    }
+
+    /// 返回遮蔽后的 API Key（用于日志输出）
+    ///
+    /// 显示前4位和后4位，中间用 `...` 代替
+    /// 如果 key 长度不足8位，则返回 `***`
+    pub fn masked_key(&self) -> String {
+        if self.api_key.len() > 8 {
+            format!(
+                "{}...{}",
+                &self.api_key[..4],
+                &self.api_key[self.api_key.len() - 4..]
+            )
+        } else {
+            "***".to_string()
+        }
+    }
+}
+
+/// 认证策略
+///
+/// 不同供应商使用不同的认证方式
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AuthStrategy {
+    /// Anthropic 认证方式
+    /// - Header: `x-api-key: <api_key>`
+    /// - Header: `anthropic-version: 2023-06-01`
+    Anthropic,
+
+    /// Bearer Token 认证方式（OpenAI 等）
+    /// - Header: `Authorization: Bearer <api_key>`
+    Bearer,
+
+    /// Google 认证方式
+    /// - Header: `x-goog-api-key: <api_key>`
+    Google,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_masked_key_long() {
+        let auth = AuthInfo::new("sk-1234567890abcdef".to_string(), AuthStrategy::Bearer);
+        assert_eq!(auth.masked_key(), "sk-1...cdef");
+    }
+
+    #[test]
+    fn test_masked_key_short() {
+        let auth = AuthInfo::new("short".to_string(), AuthStrategy::Bearer);
+        assert_eq!(auth.masked_key(), "***");
+    }
+
+    #[test]
+    fn test_masked_key_exactly_8() {
+        let auth = AuthInfo::new("12345678".to_string(), AuthStrategy::Bearer);
+        assert_eq!(auth.masked_key(), "***");
+    }
+
+    #[test]
+    fn test_masked_key_9_chars() {
+        let auth = AuthInfo::new("123456789".to_string(), AuthStrategy::Bearer);
+        assert_eq!(auth.masked_key(), "1234...6789");
+    }
+
+    #[test]
+    fn test_auth_strategy_equality() {
+        assert_eq!(AuthStrategy::Anthropic, AuthStrategy::Anthropic);
+        assert_ne!(AuthStrategy::Anthropic, AuthStrategy::Bearer);
+        assert_ne!(AuthStrategy::Bearer, AuthStrategy::Google);
+    }
+}