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/validate-static-assets.js

@@ -0,0 +1,21 @@
+'use strict';
+var fs = require('fs');
+function read(path) { return fs.readFileSync(path, 'utf8'); }
+function json(path) { return JSON.parse(read(path)); }
+function assert(name, condition) { if (!condition) { throw new Error('FAILED: ' + name); } console.log('OK:', name); }
+var packageJson = json('package.json');
+var solution = json('config/package-solution.json').solution;
+var manifest = json('src/extensions/currentNavigation/CurrentNavigationApplicationCustomizer.manifest.json');
+var app = read('src/extensions/currentNavigation/CurrentNavigationApplicationCustomizer.ts');
+var renderer = read('src/extensions/currentNavigation/CurrentNavigationRenderer.ts');
+var service = read('src/services/CurrentNavigationTaxonomyService.ts');
+assert('package version', packageJson.version === '1.0.0');
+assert('solution version', solution.version === '1.0.0.0');
+assert('tenant deployment', solution.skipFeatureDeployment === true);
+assert('component type', manifest.extensionType === 'ApplicationCustomizer');
+assert('safe renderer', renderer.indexOf('innerHTML') < 0 && app.indexOf('innerHTML') < 0);
+assert('placeholder lifecycle cleanup', app.indexOf('changedEvent.remove') >= 0);
+assert('local properties loaded', service.indexOf('LocalCustomProperties') >= 0);
+assert('root property present', read('src/services/CurrentNavigationCore.ts').indexOf('CurrentNavigation.Root') >= 0);
+assert('hidden property present', read('src/services/CurrentNavigationCore.ts').indexOf('CurrentNavigation.Hidden') >= 0);
+console.log('CurrentNavigation static tests passed.');