Navigation follow-ups: Learn link and tidier menu

Getting around the app is a little smoother, whether you are signed in or just looking around.

What changed

• Learn in the top bar. A Learn link now sits in the top bar, and Learn is also a page you can jump to from the command palette.
• A tidier command palette. When empty, Charts and tools and Guides are listed from A to Z. Search results are grouped by type, with the best match first. It shows the same plan badge as the sidebar.
• Hide the menu completely. One toggle at the far left of the top bar hides the sidebar entirely. A keyboard shortcut does the same.
• Tab reaches every sidebar row, and the arrow keys still work.
• Sidebar search is cleaner, with a simple Search hint and a search box and expand-all button of equal height.
• Signed-out visitors now get a top bar with Log in and Join free on public app pages. Market cap and dominance in the price strip now load for them too, and the short Join free label stays until wider screens, so the price in the strip stays fully visible.