Improve Web UI with footer, icon buttons, and better modals

- Add footer with author info (name, email, git repository link)
- Replace device action buttons with icons to save space:
  - Start/Stop: ▶️/⏹️, Settings: ⚙️, Calibrate: 📐, Remove: 🗑️
  - Added hover tooltips with translated text
  - Added btn-icon CSS class for compact styling
- Replace native browser confirm() with custom modal dialog:
  - Matches app theme and supports translations
  - Used for logout and device removal confirmations
  - Added confirm.title, confirm.yes, confirm.no translations
- Disable background scrolling when modals are open:
  - Added modal-open class to body when any modal opens
  - Prevents page scroll behind modals for better UX
  - Applied to all modals: login, settings, calibration, confirmation

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/src/wled_controller/static/locales/en.json

@@ -112,5 +112,8 @@
   "server.offline": "Server offline",
   "error.unauthorized": "Unauthorized - please login",
   "error.network": "Network error",
-  "error.unknown": "An error occurred"
+  "error.unknown": "An error occurred",
+  "confirm.title": "Confirm Action",
+  "confirm.yes": "Yes",
+  "confirm.no": "No"
 }