Improved Help Docs with clearer layout and smoother navigation

We’ve refreshed the Help Docs page to make it easier and more enjoyable to browse. The layout and styling now mirror the familiar pattern from our Changelog page, so everything feels consistent and easy on the eyes.

**Easier navigation and cleaner notifications**
You’ll notice we swapped the old dropdown menu with a shared, more intuitive RepoSwitcher component, making it simpler to switch between sources. We also replaced disruptive alert popups with gentle toast notifications that keep you informed without interrupting your flow.

**Better organization and feedback**
Each source now shows an expandable list of subpages, so finding related information is a breeze. Loading and empty states give you clear feedback about the page status, so you’re never left wondering if something is happening behind the scenes. Plus, tab navigation now remembers your place through the URL, helping you jump back right where you left off.