feat: иконки для Chrome и Firefox расширений

- extension/icons/ + extension-firefox/icons/
  - icon16.png (16x16), icon48.png (48x48), icon128.png (128x128)
  - взяты из frontend/public/assets/app-icons/
  - 48x48 сгенерирован из 64x64 через ImageMagick
- Манифесты: default_icon + icons секции для обоих браузеров
- build.sh: иконки включаются в zip/xpi архивы

scripts/build.sh

@@ -49,13 +49,13 @@ build_chrome_extension() {
     return 1
   fi
 
-  # Create a clean zip: manifest.json, background.js, popup/*
-  # Exclude any hidden files, icons (not needed for dev install), and OS junk
+  # Create a clean zip: manifest.json, background.js, popup/*, icons/*
   cd "$ext_dir"
   zip -r "../$out_file" \
     manifest.json \
     background.js \
     popup/ \
+    icons/ \
     -x "*/.DS_Store" "*/Thumbs.db" "*/__MACOSX/*" "*/.git/*"
   cd ..
 
@@ -76,12 +76,13 @@ build_firefox_extension() {
   fi
 
   # Firefox xpi is a zip with .xpi extension
-  # Must include manifest.json at root
+  # Must include manifest.json at root + icons
   cd "$ext_dir"
   zip -r "../$out_file" \
     manifest.json \
     background.js \
     popup/ \
+    icons/ \
     -x "*/.DS_Store" "*/Thumbs.db" "*/__MACOSX/*" "*/.git/*"
   cd ..