feat(scripts): add github-traffic.mjs for repo traffic insights

Zero-dep Node script that fetches the four GitHub Traffic endpoints
(views, clones, popular referrers, popular paths) plus core repo stats,
and prints a formatted report or raw JSON. Supports --save to append
JSONL snapshots so daily runs can build a >14-day history beyond the
GitHub API's retention window.

Wired as `npm run traffic`. Requires GITHUB_TOKEN with push access.

package.json

@@ -9,7 +9,8 @@
   },
   "scripts": {
     "start": "node server.mjs",
-    "setup": "node setup.mjs"
+    "setup": "node setup.mjs",
+    "traffic": "node scripts/github-traffic.mjs"
   },
   "keywords": [
     "openclaw",