feat: add logo and polish icon presentation

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

extension/manifest.firefox.json

@@ -3,6 +3,11 @@
   "name": "idfoto",
   "version": "0.1.0",
   "description": "Two-factor encrypted password manager",
+  "icons": {
+    "16": "icons/icon-16.png",
+    "48": "icons/icon-48.png",
+    "128": "icons/icon-128.png"
+  },
   "browser_specific_settings": {
     "gecko": {
       "id": "idfoto@adlee.work",