feat: enhance current duty display with remaining time and improved contact links

- Added a new message key for displaying remaining time until the end of the shift in both English and Russian.
- Updated the current duty card to show remaining time with a formatted string.
- Enhanced the contact links to support block layout with icons for phone and Telegram, improving visual presentation.
- Implemented a new utility function to calculate remaining time until the end of the shift.
- Added unit tests for the new functionality, ensuring accurate time calculations and proper rendering of contact links.

webapp/js/i18n.js

@@ -58,6 +58,7 @@ export const MESSAGES = {
     "current_duty.title": "Current Duty",
     "current_duty.no_duty": "No one is on duty right now",
     "current_duty.shift": "Shift",
+    "current_duty.remaining": "Remaining: {hours}h {minutes}min",
     "current_duty.back": "Back to calendar"
   },
   ru: {
@@ -112,6 +113,7 @@ export const MESSAGES = {
     "current_duty.title": "Текущее дежурство",
     "current_duty.no_duty": "Сейчас никто не дежурит",
     "current_duty.shift": "Смена",
+    "current_duty.remaining": "Осталось: {hours}ч {minutes}мин",
     "current_duty.back": "Назад к календарю"
   }
 };