feat: implement internationalization for duty calendar

- Introduced a new `i18n.js` module for handling translations and language detection, supporting both Russian and English.
- Updated various components to utilize the new translation functions, enhancing user experience by providing localized messages for errors, hints, and UI elements.
- Refactored existing code in `api.js`, `calendar.js`, `dutyList.js`, `hints.js`, and `ui.js` to replace hardcoded strings with translated messages, improving maintainability and accessibility.
- Enhanced the initialization process in `main.js` to set the document language and update UI elements based on the user's language preference.

webapp/js/dutyList.js

@@ -3,7 +3,7 @@
  */
 
 import { dutyListEl, state } from "./dom.js";
-import { EVENT_TYPE_LABELS } from "./constants.js";
+import { t } from "./i18n.js";
 import { escapeHtml } from "./utils.js";
 import {
   localDateString,
@@ -33,9 +33,10 @@ export function dutyTimelineCardHtml(d, isCurrent) {
   } else {
     timeStr = startDDMM + " " + startTime + " – " + endDDMM + " " + endTime;
   }
+  const lang = state.lang;
   const typeLabel = isCurrent
-    ? "Сейчас дежурит"
-    : (EVENT_TYPE_LABELS[d.event_type] || "Дежурство");
+    ? t(lang, "duty.now_on_duty")
+    : (t(lang, "event_type." + (d.event_type || "duty")));
   const extraClass = isCurrent ? " duty-item--current" : "";
   return (
     '<div class="duty-item duty-item--duty duty-timeline-card' +
@@ -59,15 +60,16 @@ export function dutyTimelineCardHtml(d, isCurrent) {
  * @returns {string}
  */
 export function dutyItemHtml(d, typeLabelOverride, showUntilEnd, extraClass) {
+  const lang = state.lang;
   const typeLabel =
     typeLabelOverride != null
       ? typeLabelOverride
-      : (EVENT_TYPE_LABELS[d.event_type] || d.event_type);
+      : (t(lang, "event_type." + (d.event_type || "duty")));
   let itemClass = "duty-item duty-item--" + (d.event_type || "duty");
   if (extraClass) itemClass += " " + extraClass;
   let timeOrRange = "";
   if (showUntilEnd && d.event_type === "duty") {
-    timeOrRange = "до " + formatTimeLocal(d.end_at);
+    timeOrRange = t(lang, "duty.until", { time: formatTimeLocal(d.end_at) });
   } else if (d.event_type === "vacation" || d.event_type === "unavailable") {
     const startStr = formatDateKey(d.start_at);
     const endStr = formatDateKey(d.end_at);
@@ -98,7 +100,7 @@ export function renderDutyList(duties) {
   const filtered = duties.filter((d) => d.event_type === "duty");
   if (filtered.length === 0) {
     dutyListEl.classList.remove("duty-timeline");
-    dutyListEl.innerHTML = '<p class="muted">В этом месяце дежурств нет.</p>';
+    dutyListEl.innerHTML = '<p class="muted">' + t(state.lang, "duty.none_this_month") + "</p>";
     return;
   }
   dutyListEl.classList.add("duty-timeline");
@@ -121,7 +123,9 @@ export function renderDutyList(duties) {
       "duty-timeline-day" + (isToday ? " duty-timeline-day--today" : "");
     const dateLabel = dateKeyToDDMM(date);
     const dateCellHtml = isToday
-      ? '<span class="duty-timeline-date"><span class="duty-timeline-date-label">Сегодня</span><span class="duty-timeline-date-day">' +
+      ? '<span class="duty-timeline-date"><span class="duty-timeline-date-label">' +
+        escapeHtml(t(state.lang, "duty.today")) +
+        '</span><span class="duty-timeline-date-day">' +
         escapeHtml(dateLabel) +
         '</span><span class="duty-timeline-date-dot" aria-hidden="true"></span></span>'
       : '<span class="duty-timeline-date">' + escapeHtml(dateLabel) + "</span>";