feat: 初始化项目基础架构和核心功能

- 添加项目基础结构：Cargo.toml、.gitignore、设备UID和密钥文件
- 实现前端Vue3项目结构：路由、登录页面、设备管理页面
- 添加核心协议定义(crates/protocol)：设备状态、资产、USB事件等
- 实现客户端监控模块：系统状态收集、资产收集
- 实现服务端基础API和插件系统
- 添加数据库迁移脚本：设备管理、资产跟踪、告警系统等
- 实现前端设备状态展示和基本交互
- 添加使用时长统计和水印功能插件

crates/server/src/alert.rs

@@ -0,0 +1,118 @@
+use crate::AppState;
+use tracing::{info, warn, error};
+
+/// Background task for data cleanup and alert processing
+pub async fn cleanup_task(state: AppState) {
+    let mut interval = tokio::time::interval(tokio::time::Duration::from_secs(3600));
+
+    loop {
+        interval.tick().await;
+
+        // Cleanup old status history
+        if let Err(e) = sqlx::query(
+            "DELETE FROM device_status_history WHERE reported_at < datetime('now', ?)"
+        )
+        .bind(format!("-{} days", state.config.retention.status_history_days))
+        .execute(&state.db)
+        .await
+        {
+            error!("Failed to cleanup status history: {}", e);
+        }
+
+        // Cleanup old USB events
+        if let Err(e) = sqlx::query(
+            "DELETE FROM usb_events WHERE event_time < datetime('now', ?)"
+        )
+        .bind(format!("-{} days", state.config.retention.usb_events_days))
+        .execute(&state.db)
+        .await
+        {
+            error!("Failed to cleanup USB events: {}", e);
+        }
+
+        // Cleanup handled alert records
+        if let Err(e) = sqlx::query(
+            "DELETE FROM alert_records WHERE handled = 1 AND triggered_at < datetime('now', ?)"
+        )
+        .bind(format!("-{} days", state.config.retention.alert_records_days))
+        .execute(&state.db)
+        .await
+        {
+            error!("Failed to cleanup alert records: {}", e);
+        }
+
+        // Mark devices as offline if no heartbeat for 2 minutes
+        if let Err(e) = sqlx::query(
+            "UPDATE devices SET status = 'offline' WHERE status = 'online' AND last_heartbeat < datetime('now', '-2 minutes')"
+        )
+        .execute(&state.db)
+        .await
+        {
+            error!("Failed to mark stale devices offline: {}", e);
+        }
+
+        // SQLite WAL checkpoint
+        if let Err(e) = sqlx::query("PRAGMA wal_checkpoint(TRUNCATE)")
+            .execute(&state.db)
+            .await
+        {
+            warn!("WAL checkpoint failed: {}", e);
+        }
+
+        info!("Cleanup cycle completed");
+    }
+}
+
+/// Send email notification
+pub async fn send_email(
+    smtp_config: &crate::config::SmtpConfig,
+    to: &str,
+    subject: &str,
+    body: &str,
+) -> anyhow::Result<()> {
+    use lettre::message::header::ContentType;
+    use lettre::{Message, SmtpTransport, Transport};
+    use lettre::transport::smtp::authentication::Credentials;
+
+    let email = Message::builder()
+        .from(smtp_config.from.parse()?)
+        .to(to.parse()?)
+        .subject(subject)
+        .header(ContentType::TEXT_HTML)
+        .body(body.to_string())?;
+
+    let creds = Credentials::new(
+        smtp_config.username.clone(),
+        smtp_config.password.clone(),
+    );
+
+    let mailer = SmtpTransport::starttls_relay(&smtp_config.host)?
+        .port(smtp_config.port)
+        .credentials(creds)
+        .build();
+
+    mailer.send(&email)?;
+    Ok(())
+}
+
+/// Shared HTTP client for webhook notifications.
+/// Lazily initialized once and reused across calls to benefit from connection pooling.
+static WEBHOOK_CLIENT: std::sync::OnceLock<reqwest::Client> = std::sync::OnceLock::new();
+
+fn webhook_client() -> &'static reqwest::Client {
+    WEBHOOK_CLIENT.get_or_init(|| {
+        reqwest::Client::builder()
+            .timeout(std::time::Duration::from_secs(10))
+            .build()
+            .unwrap_or_else(|_| reqwest::Client::new())
+    })
+}
+
+/// Send webhook notification
+pub async fn send_webhook(url: &str, payload: &serde_json::Value) -> anyhow::Result<()> {
+    webhook_client().post(url)
+        .json(payload)
+        .send()
+        .await?;
+    Ok(())
+}