refactor: extract navbar and footer into reusable handlebars partials

- Replace duplicated navbar markup across all HTML pages with {{> navbar }} partial
- Replace duplicated footer markup across all HTML pages with {{> footer }} partial
- Add TypeScript type definitions for vite-plugin-handlebars integration
- Update vite.config.ts to support handlebars partial compilation
- Update tsconfig.json to include handlebars type definitions
- Update nginx.conf for proper static file serving with partials
- Update translation files for de, pt, tr, vi, and zh-TW locales
- Reduce code duplication and improve maintainability across 13+ HTML pages
- Ensure consistent navbar and footer behavior across the entire application

src/types/vite-plugin-handlebars.d.ts

@@ -0,0 +1 @@
+declare module 'vite-plugin-handlebars';