feat: site-wide restructure and some cleanup

[muhdfdeen]

File Structure Improvements

• Modified the astro.config.mjs to set up the sidebar content manually.
• Renamed all the content folders to be lowercase and make more sense (like project is now getting-started).
• Added new index.mdx pages for each main section so they have a proper landing page.
• Consolidated Extras and Performance pages into other main sections.
• Added two new subfolders under assets/ for better scalability.

Cleanup

• Cleaned up package.json and removed a bunch of Vue packages we weren't using anymore.
• Removed slug values from each MDX file's frontmatter as it can be automatically generated based on file path.
• Removed the starlight-heading-badges plugin since Starlight's built-in Badges component does pretty much the same thing.
• Updated README.md to use logo at the beginning of the file.
• Got rid of the unused src/components/sidebar.astro file (we're using the one with the capital 'S').

Content Fixes

• Changed all HTML <img> tags to Astro's <Image> component for automatic image optimization.
• Updated most content files' frontmatter (like topic, lastUpdated, etc.) so they're all consistent.
• Fixed all the internal links and slugs everywhere to match the new folder names.
• Changed all the old badge syntax to use the standard Starlight <Badge> component.
• Deleted a bunch of old/unneeded pages to clean things up (like auctionhouse.mdx, dukesmart.mdx, and others).