chore: fix vue-tsc error in ci-tools conditional header spread

`body` is `unknown`, so `...(body && {...})` spreads a string-including
union and fails vue-tsc (TS2698). `Boolean(body)` keeps the spread
object-only while preserving the runtime behavior.

Assisted-by: claude-code:opus-4.8

tools/ci-tools.ts

@@ -83,7 +83,7 @@ async function setPrLabels(): Promise<void> {
         Accept: 'application/vnd.github+json',
         Authorization: `Bearer ${env.GITHUB_TOKEN}`,
         'X-GitHub-Api-Version': '2022-11-28',
-        ...(body && {'Content-Type': 'application/json'}),
+        ...(Boolean(body) && {'Content-Type': 'application/json'}),
       },
       body: body ? JSON.stringify(body) : undefined,
     });