feat(proxy): implement local HTTP proxy server with multi-provider failover

Add a complete HTTP proxy server implementation built on Axum framework,
enabling local API request forwarding with automatic provider failover
and load balancing capabilities.

Backend Implementation (Rust):
- Add proxy server module with 7 core components:
  * server.rs: Axum HTTP server lifecycle management (start/stop/status)
  * router.rs: API routing configuration for Claude/OpenAI/Gemini endpoints
  * handlers.rs: Request/response handling and transformation
  * forwarder.rs: Upstream forwarding logic with retry mechanism (652 lines)
  * error.rs: Comprehensive error handling and HTTP status mapping
  * types.rs: Shared types (ProxyConfig, ProxyStatus, ProxyServerInfo)
  * health.rs: Provider health check infrastructure

Service Layer:
- Add ProxyService (services/proxy.rs, 157 lines):
  * Manage proxy server lifecycle
  * Handle configuration updates
  * Track runtime status and metrics

Database Layer:
- Add proxy configuration DAO (dao/proxy.rs, 242 lines):
  * Persist proxy settings (listen address, port, timeout)
  * Store provider priority and availability flags
- Update schema with proxy_config table (schema.rs):
  * Support runtime configuration persistence

Tauri Commands:
- Add 6 command endpoints (commands/proxy.rs):
  * start_proxy_server: Launch proxy server
  * stop_proxy_server: Gracefully shutdown server
  * get_proxy_status: Query runtime status
  * get_proxy_config: Retrieve current configuration
  * update_proxy_config: Modify settings without restart
  * is_proxy_running: Check server state

Frontend Implementation (React + TypeScript):
- Add ProxyPanel component (222 lines):
  * Real-time server status display
  * Start/stop controls
  * Provider availability monitoring
- Add ProxySettingsDialog component (420 lines):
  * Configuration editor (address, port, timeout)
  * Provider priority management
  * Settings validation
- Add React hooks:
  * useProxyConfig: Manage proxy configuration state
  * useProxyStatus: Poll and display server status
- Add TypeScript types (types/proxy.ts):
  * Define ProxyConfig, ProxyStatus interfaces

Provider Integration:
- Extend Provider model with availability field (providers.rs):
  * Track provider health for failover logic
- Update ProviderCard UI to display proxy status
- Integrate proxy controls in Settings page

Dependencies:
- Add Axum 0.7 (async web framework)
- Add Tower 0.4 (middleware and service abstractions)
- Add Tower-HTTP (CORS layer)
- Add Tokio sync primitives (oneshot, RwLock)

Technical Details:
- Graceful shutdown via oneshot channel
- Shared state with Arc<RwLock<T>> for thread-safe config updates
- CORS enabled for cross-origin frontend access
- Request/response streaming support
- Automatic retry with exponential backoff (forwarder)
- API key extraction from multiple config formats (Claude/Codex/Gemini)

File Statistics:
- 41 files changed
- 3491 insertions(+), 41 deletions(-)
- Core modules: 1393 lines (server + forwarder + handlers)
- Frontend UI: 642 lines (ProxyPanel + ProxySettingsDialog)
- Database/DAO: 326 lines

This implementation provides the foundation for advanced features like:
- Multi-provider load balancing
- Automatic failover on provider errors
- Request logging and analytics
- Usage tracking and cost monitoring

src-tauri/src/database/schema.rs

@@ -31,12 +31,19 @@ impl Database {
                 icon_color TEXT,
                 meta TEXT NOT NULL DEFAULT '{}',
                 is_current BOOLEAN NOT NULL DEFAULT 0,
+                is_proxy_target BOOLEAN NOT NULL DEFAULT 0,
                 PRIMARY KEY (id, app_type)
             )",
             [],
         )
         .map_err(|e| AppError::Database(e.to_string()))?;
 
+        // 尝试添加 is_proxy_target 列（如果表已存在但缺少该列）
+        let _ = conn.execute(
+            "ALTER TABLE providers ADD COLUMN is_proxy_target BOOLEAN NOT NULL DEFAULT 0",
+            [],
+        );
+
         // 2. Provider Endpoints 表
         conn.execute(
             "CREATE TABLE IF NOT EXISTS provider_endpoints (
@@ -120,6 +127,83 @@ impl Database {
         )
         .map_err(|e| AppError::Database(e.to_string()))?;
 
+        // 8. Proxy Config 表 (代理服务器配置)
+        // 代理配置表（单例）
+        conn.execute(
+            "CREATE TABLE IF NOT EXISTS proxy_config (
+                id INTEGER PRIMARY KEY CHECK (id = 1),
+                enabled INTEGER NOT NULL DEFAULT 0,
+                listen_address TEXT NOT NULL DEFAULT '127.0.0.1',
+                listen_port INTEGER NOT NULL DEFAULT 5000,
+                max_retries INTEGER NOT NULL DEFAULT 3,
+                request_timeout INTEGER NOT NULL DEFAULT 300,
+                enable_logging INTEGER NOT NULL DEFAULT 1,
+                target_app TEXT NOT NULL DEFAULT 'claude',
+                created_at TEXT NOT NULL DEFAULT (datetime('now')),
+                updated_at TEXT NOT NULL DEFAULT (datetime('now'))
+            )",
+            [],
+        )
+        .map_err(|e| AppError::Database(e.to_string()))?;
+
+        // 尝试添加 target_app 列（如果表已存在但缺少该列）
+        // 忽略 "duplicate column name" 错误
+        let _ = conn.execute(
+            "ALTER TABLE proxy_config ADD COLUMN target_app TEXT NOT NULL DEFAULT 'claude'",
+            [],
+        );
+
+        // 9. Provider Health 表 (Provider健康状态)
+        conn.execute(
+            "CREATE TABLE IF NOT EXISTS provider_health (
+                provider_id TEXT NOT NULL,
+                app_type TEXT NOT NULL,
+                is_healthy INTEGER NOT NULL DEFAULT 1,
+                consecutive_failures INTEGER NOT NULL DEFAULT 0,
+                last_success_at TEXT,
+                last_failure_at TEXT,
+                last_error TEXT,
+                updated_at TEXT NOT NULL,
+                PRIMARY KEY (provider_id, app_type),
+                FOREIGN KEY (provider_id, app_type) REFERENCES providers(id, app_type) ON DELETE CASCADE
+            )",
+            [],
+        )
+        .map_err(|e| AppError::Database(e.to_string()))?;
+
+        // 10. Proxy Usage 表 (代理使用统计，可选)
+        conn.execute(
+            "CREATE TABLE IF NOT EXISTS proxy_usage (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                provider_id TEXT NOT NULL,
+                app_type TEXT NOT NULL,
+                endpoint TEXT NOT NULL,
+                request_tokens INTEGER,
+                response_tokens INTEGER,
+                status_code INTEGER NOT NULL,
+                latency_ms INTEGER NOT NULL,
+                error TEXT,
+                timestamp TEXT NOT NULL
+            )",
+            [],
+        )
+        .map_err(|e| AppError::Database(e.to_string()))?;
+
+        // 为 proxy_usage 创建索引
+        conn.execute(
+            "CREATE INDEX IF NOT EXISTS idx_proxy_usage_timestamp
+             ON proxy_usage(timestamp)",
+            [],
+        )
+        .map_err(|e| AppError::Database(e.to_string()))?;
+
+        conn.execute(
+            "CREATE INDEX IF NOT EXISTS idx_proxy_usage_provider
+             ON proxy_usage(provider_id, app_type)",
+            [],
+        )
+        .map_err(|e| AppError::Database(e.to_string()))?;
+
         Ok(())
     }