Add author to the manifest for the Quattro contract

The documented plugin manifest contract (docs/omarchy-shell.md) and every
first-party manifest include author; the publishing validation rejects a
manifest without it.

manifest.json

@@ -3,6 +3,7 @@
   "id": "felixzsh.key-visualizer",
   "name": "Key Visualizer",
   "version": "1.5.0",
+  "author": "felixzsh",
   "description": "Shows the keys you press on screen. Great for keybinding tutorials, demos, and screencasts.",
   "kinds": [
     "panel",