Migrate GuideChimp to Vite and Vitest

[v-rudkovskiy]

• replace Webpack with Vite
• replace Karma and Jasmine with Vitest and happy-dom
• preserve UMD, CommonJS, minified CSS/JS, and source map outputs
• build GuideChimp core and plugins using Vite
• add Vite watch mode for development
• migrate deprecated Sass imports to the module system
• remove obsolete Webpack, Karma, and Babel dependencies
• add an interactive English demo page
• document the local demo command
• fix vulnerabilities