Add author auth, forking, tags, and stats tracking

Introduce token-based author authentication (register/verify API),
   skill forking with EditGate protection, tag metadata on skills,
   and download/push stats. Enhanced push scripts with token auth
   and per-skill filtering. Updated UI with stats, tags, and
   author info on skill cards.

data/stats.json

@@ -0,0 +1,7 @@
+{
+  "example-skill": {
+    "downloads": 0,
+    "pushes": 1,
+    "lastPushedAt": "2026-02-12T13:27:13.727Z"
+  }
+}