Add automatic sidebar generation with template support

[Josephat-S]

This pull request adds support for generating a customizable sidebar navigation component with icons for selected templates. It introduces an icon mapping for sidebar items, generates a Sidebar.tsx component with appropriate icons and navigation links when the template supports sidebars, and ensures the sidebar is only created if requested in the config.

Sidebar navigation generation:

• Adds an ICON_MAP object mapping common sidebar item labels to Lucide icon names, and a SIDEBAR_TEMPLATES array listing templates that support sidebar navigation. (src/navigation.js)
• Implements the generateSidebarComponent function that generates a Sidebar.tsx React component, including logic for importing icons, rendering nav links with icons, and highlighting the active link. (src/navigation.js)
• Updates the generateNavigation function to generate the Sidebar.tsx file in the appropriate directory if the template supports sidebars and the user has opted to include one. (src/navigation.js)…e template to support it

Closes #88