Move config out of the plugin dir so edits don't reload the plugin

The shell watches every file under ~/.config/omarchy/plugins/ with
inotify (no extension filter) and reloads all plugin code on any change,
so config.json there made every edit tear down and rebuild the panel and
bar widget. Config now lives at ~/.config/omarchy/key-visualizer.json, which
is not watched: edits update the display live. The panel migrates the
old plugin-dir config (values carried over, file removed) on first load
after the update.

manifest.json

@@ -2,7 +2,7 @@
   "schemaVersion": 1,
   "id": "felixzsh.key-visualizer",
   "name": "Key Visualizer",
-  "version": "1.3.0",
+  "version": "1.3.1",
   "description": "Shows the keys you press on screen. Great for keybinding tutorials, demos, and screencasts.",
   "kinds": [
     "panel",