New docs structure (#41919)

New docs structure (#41919)

* Reorganize documentation structure

Getting Started:
- Simplify introduction.mdx to focus on basics
- Add install.mdx with package manager instructions
- Move approach.mdx from Extend to Getting Started
- Delete best-practices.mdx (merged elsewhere)
- Update javascript.mdx

Guides:
- Add quickstart.mdx for CDN-based quick start
- Add npm.mdx guide with screenshots
- Update parcel, vite, webpack guides

Extend:
- Remove approach.mdx (moved to Getting Started)
- Remove icons.mdx

Sidebar:
- Restructure navigation to reflect new organization
- Add Install and Approach to Getting Started
- Add Quickstart and npm to Guides

Also includes minor doc updates:
- customize/sass.mdx
- utilities/background.mdx
- utilities/colors.mdx

* Optimised images with calibre/image-actions

* fix broken link and update sidebar

* Optimised images with calibre/image-actions

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>