Add documentation site with GitHub Pages deployment

[psd-coder]

Overview

Introduces a documentation site for the project, built with Astro and deployed automatically to GitHub Pages on pushes to
main.

Problem Statement

The project lacked public-facing documentation, making it harder for users to understand the API and usage patterns.

Solution Approach

• Added a docs/ workspace with an Astro-based site using a custom docs theme
• Wrote initial documentation covering the library's API in a single MDX page
• Added a CI workflow that builds and deploys the docs to GitHub Pages via OIDC trusted publishing
• Excluded docs/ from the root workspace scripts to keep the main build unaffected

Breaking Changes

None.

[github-actions]

size-limit report 📦

Path	Size
createTypedChannel	254 B (0%)
createPostMessageTransport	86 B (0%)
createEventTargetTransport	109 B (0%)