fix: resolve pre-existing TypeScript errors in alerts and page

Add missing checkInterval to AlertConfig, targetAgents to AlertRule,
and replace invalid SVG title prop with aria-label.

app/alerts/page.tsx

@@ -16,6 +16,7 @@ interface AlertConfig {
   enabled: boolean;
   receiveAgent: string;
   rules: AlertRule[];
+  checkInterval?: number;
 }
 
 interface Agent {

app/api/alerts/check/route.ts

@@ -10,6 +10,7 @@ interface AlertRule {
   name: string;
   enabled: boolean;
   threshold?: number;
+  targetAgents?: string[];
 }
 
 interface AlertConfig {

app/page.tsx

@@ -274,7 +274,7 @@ function MiniSparkline({ data, width = 120, height = 24, color: fixedColor }: {
   const id = `spark-${Math.random().toString(36).slice(2, 8)}`;
   return (
     <span className="inline-flex items-center gap-1">
-      <svg width={width} height={height} className="inline-block align-middle" title={data.map(v => v ? formatMs(v) : '-').join(' → ')}>
+      <svg width={width} height={height} className="inline-block align-middle" aria-label={data.map(v => v ? formatMs(v) : '-').join(' → ')}>
         <defs>
           <linearGradient id={id} x1="0" y1="0" x2="0" y2="1">
             <stop offset="0%" stopColor={color} stopOpacity={0.3} />