Add Recurring Events Web Part with data service and UI components

- Implement RecurringEventsDataService for fetching events from SharePoint lists.
- Define types for events and categories in RecurringEventsTypes.
- Create RecurringEventsWebPart to manage properties and render events.
- Develop UI components for displaying events in filmstrip and compact layouts.
- Add localization support for English and German languages.
- Implement tests for core functionalities related to event handling.
- Set up TypeScript and TSLint configurations for the project.

tests/RecurringEventsCore.test.ts

@@ -0,0 +1,40 @@
+import {
+  calculateDateRange,
+  filterAndSortEvents,
+  getMonthAnchors,
+  normalizeAssetUrl,
+  normalizeMaxEvents,
+  normalizeRangeDays,
+  parseSharePointDate
+} from '../src/webparts/recurringEvents/RecurringEventsCore';
+import { IEventDateRange, IRecurringEvent } from '../src/webparts/recurringEvents/RecurringEventsTypes';
+
+declare const console: { log(message: string): void };
+let passed: number = 0;
+function assert(condition: boolean, message: string): void { if (!condition) { throw new Error(message); } passed++; }
+function event(key: string, day: number, type: number, category: string): IRecurringEvent {
+  return {
+    key: key, id: 1, title: key + '-' + type,
+    start: new Date(2026, 7, day, 10), end: new Date(2026, 7, day, 11), allDay: false,
+    location: '', category: category, description: '', imageUrl: '', detailsUrl: '', recurring: true, eventType: type
+  };
+}
+
+const range: IEventDateRange = calculateDateRange(30, new Date(2026, 7, 10, 15));
+assert(range.start.getHours() === 0 && range.start.getDate() === 10, 'Range must start at local midnight.');
+assert(range.end.getDate() === 9 && range.end.getMonth() === 8, '30-day range end is invalid.');
+assert(normalizeRangeDays(14) === 14 && normalizeRangeDays(13) === 30, 'Range values must be constrained.');
+assert(normalizeMaxEvents(0) === 10 && normalizeMaxEvents(80) === 50, 'Maximum event count must be constrained.');
+assert(getMonthAnchors(new Date(2026, 6, 1), new Date(2026, 8, 1)).length === 3, 'Every affected month must be queried.');
+assert(parseSharePointDate('2026-08-24 10:30:00').getUTCMinutes() === 30, 'SOAP UTC date must be parsed as UTC.');
+assert(normalizeAssetUrl('javascript:alert(1)', 'http://portal') === '', 'Unsafe image URL must be rejected.');
+assert(normalizeAssetUrl('/SiteAssets/event.jpg', 'http://portal') === '/SiteAssets/event.jpg', 'Relative image URL must be retained.');
+
+const filtered: IRecurringEvent[] = filterAndSortEvents([
+  event('series|1', 12, 1, 'Work'), event('series|1', 12, 4, 'Work'),
+  event('deleted', 13, 3, 'Work'), event('other', 11, 0, 'Private')
+], range, 'Work', 10);
+assert(filtered.length === 1, 'Category, deleted occurrences and duplicates must be filtered.');
+assert(filtered[0].eventType === 4, 'A modified occurrence must override its generated occurrence.');
+
+console.log('Recurring events core tests passed: ' + passed);