feat: 新增 target description 字段，收紧 id/name 长度，调整延迟列和名称列

tests/server/checker/engine.test.ts

@@ -55,6 +55,7 @@ function makeCommandTarget(name: string, overrides?: Partial<ResolvedCommandTarg
       exec: "bun",
       maxOutputBytes: 1024 * 1024,
     },
+    description: null,
     group: "default",
     id: name,
     intervalMs: 60000,
@@ -259,6 +260,7 @@ describe("ProbeEngine", () => {
 
     try {
       const httpTarget: ResolvedHttpTarget = {
+        description: null,
         group: "default",
         http: {
           headers: {},