Initial commit: AutoTrader Marker Firefox extension

Mark AutoTrader listings as 'not wanted' on both search results and detail
pages. Includes the unlisted signing / auto-update pipeline (web-ext +
dist/updates.json polled by Firefox).

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

icon.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64">
+  <rect width="64" height="64" rx="12" fill="#1e1e1e"/>
+  <path d="M18 22 L46 22 L42 42 L22 42 Z" fill="#c41e1e" stroke="#fff" stroke-width="2" stroke-linejoin="round"/>
+  <circle cx="26" cy="48" r="3" fill="#fff"/>
+  <circle cx="38" cy="48" r="3" fill="#fff"/>
+  <path d="M20 22 L44 22 M22 30 L42 30" stroke="#fff" stroke-width="1.5" opacity="0.4"/>
+  <path d="M16 16 L48 48 M48 16 L16 48" stroke="#fff" stroke-width="4" stroke-linecap="round" opacity="0.9"/>
+</svg>