Add Current Navigation Application Customizer

- Created a new SPFx Application Customizer for current navigation.
- Implemented core functionality to fetch and render navigation items from a SharePoint term set.
- Added styles for the navigation component using SCSS.
- Included localization support for English and German languages.
- Developed unit tests for core navigation functionalities.
- Configured TypeScript and TSLint settings for the project.
- Added validation scripts for static assets and package configuration.

tests/CurrentNavigationCore.test.ts

@@ -0,0 +1,47 @@
+import {
+  buildCurrentNavigationItems, getLocalProperty, parseBoolean, resolveTermUrl, selectCurrentNavigationRoot
+} from '../src/services/CurrentNavigationCore';
+import { ICurrentNavigationTerm } from '../src/services/CurrentNavigationTypes';
+
+let passed: number = 0;
+function assert(name: string, condition: boolean): void {
+  if (!condition) { throw new Error('FAILED: ' + name); }
+  passed++; console.log('OK:', name);
+}
+function term(value: any): ICurrentNavigationTerm { return value as ICurrentNavigationTerm; } // tslint:disable-line:no-any
+
+const terms: ICurrentNavigationTerm[] = [
+  term({ Id: 'root', Name: 'HR', PathOfTerm: 'HR', LocalCustomProperties: {
+    'CurrentNavigation.Root': 'true', '_Sys_Nav_SimpleLinkUrl': '/sites/portal/hr/SitePages/Home.aspx'
+  }}),
+  term({ Id: 'docs', Name: 'Dokumente', PathOfTerm: 'HR;Dokumente', LocalCustomProperties: {
+    '_Sys_Nav_SimpleLinkUrl': '/sites/portal/hr/Dokumente'
+  }}),
+  term({ Id: 'admin', Name: 'Administration', PathOfTerm: 'HR;Administration', LocalCustomProperties: {
+    'CurrentNavigation.Hidden': 'true'
+  }}),
+  term({ Id: 'secret', Name: 'Intern', PathOfTerm: 'HR;Administration;Intern', LocalCustomProperties: {} }),
+  term({ Id: 'forms', Name: 'Formulare', PathOfTerm: 'HR;Dokumente;Formulare', LocalCustomProperties: {} })
+];
+
+assert('German boolean is accepted', parseBoolean('ja'));
+assert('local property is read', getLocalProperty(terms[0], 'CurrentNavigation.Root') === 'true');
+assert('site collection token resolves', resolveTermUrl(term({
+  LocalCustomProperties: { '_Sys_Nav_SimpleLinkUrl': '~sitecollection/start' }
+}), 'https://portal/sites/a') === 'https://portal/sites/a/start');
+const root: ICurrentNavigationTerm = selectCurrentNavigationRoot(
+  terms, 'https://portal/sites/portal/hr', 'https://portal/sites/portal'
+);
+assert('root is selected through its site home URL', !!root && root.Id === 'root');
+const items = buildCurrentNavigationItems(terms, root, 'https://portal/sites/portal', 1031, 3, false);
+assert('root is not rendered by default', items.length === 1 && items[0].id === 'docs');
+assert('descendants are nested', items[0].items.length === 1 && items[0].items[0].id === 'forms');
+assert('hidden branch is removed', items.every(item => item.id !== 'admin'));
+const withRoot = buildCurrentNavigationItems(terms, root, 'https://portal/sites/portal', 1031, 3, true);
+assert('root can be rendered', withRoot.length === 1 && withRoot[0].id === 'root');
+const unordered = buildCurrentNavigationItems(
+  [terms[4], terms[1], terms[0]], root, 'https://portal/sites/portal', 1031, 3, false
+);
+assert('hierarchy is independent of taxonomy response order',
+  unordered.length === 1 && unordered[0].id === 'docs' && unordered[0].items[0].id === 'forms');
+console.log('CurrentNavigation core tests passed:', passed);