Fix pause toggle: never delete the flag file

The FileView watcher fires on content changes but not on deletion, so
resuming (rm of the flag) left the panel and the menu stuck paused.
Rewrite the flag with 0 or 1 instead, matching the state-file pattern
that already works.

manifest.json

@@ -2,7 +2,7 @@
   "schemaVersion": 1,
   "id": "felixzsh.key-visualizer",
   "name": "Key Visualizer",
-  "version": "1.3.2",
+  "version": "1.3.3",
   "description": "Shows the keys you press on screen. Great for keybinding tutorials, demos, and screencasts.",
   "kinds": [
     "panel",