fix: clear timeout timer in runSource to prevent event loop hang

The Promise.race timeout was never cleared on success/failure,
keeping the Node event loop alive for ~30s after fast sweeps.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apis/briefing.mjs

@@ -47,15 +47,18 @@ const SOURCE_TIMEOUT_MS = 30_000; // 30s max per individual source
 
 export async function runSource(name, fn, ...args) {
   const start = Date.now();
+  let timer;
   try {
     const dataPromise = fn(...args);
-    const timeoutPromise = new Promise((_, reject) =>
-      setTimeout(() => reject(new Error(`Source ${name} timed out after ${SOURCE_TIMEOUT_MS / 1000}s`)), SOURCE_TIMEOUT_MS)
-    );
+    const timeoutPromise = new Promise((_, reject) => {
+      timer = setTimeout(() => reject(new Error(`Source ${name} timed out after ${SOURCE_TIMEOUT_MS / 1000}s`)), SOURCE_TIMEOUT_MS);
+    });
     const data = await Promise.race([dataPromise, timeoutPromise]);
     return { name, status: 'ok', durationMs: Date.now() - start, data };
   } catch (e) {
     return { name, status: 'error', durationMs: Date.now() - start, error: e.message };
+  } finally {
+    clearTimeout(timer);
   }
 }