Release v0.1.2: site-backup persistence + PNG toolbar icons

- Mirror dismissals to window.localStorage on autotrader.co.uk ("atm:..."
  key). If browser.storage.local comes up empty after a quirky reinstall,
  the content script rehydrates from the site backup on the next page load.
- Replace the SVG toolbar icon with PNG renders (16/32/48/96/128) — some
  Firefox installs don't render extension SVG icons reliably in the
  toolbar / extensions flyout.
- Sharp added as a devDependency to rebuild icons from icon.svg.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "autotrader-marker",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "private": true,
   "description": "Firefox extension that marks AutoTrader listings as 'not wanted'.",
   "scripts": {
@@ -10,6 +10,7 @@
     "release:major": "bin/release.sh major"
   },
   "devDependencies": {
+    "sharp": "^0.34.5",
     "web-ext": "^8.3.0"
   }
 }