Keyboard shortcuts exist but nothing tells you

[Phantom-VK]

Problem

Ctrl/Cmd+1 through 6 switch views and Escape closes surfaces. They work perfectly. Nobody knows they exist.

Where

• hooks/useShortcuts.ts:4 -> SHORTCUT_VIEWS map lists them
• No UI hint anywhere

Fix

Add two surfaces:

1. A ? overlay (or help icon in header) listing all bindings
2. Subtle key hint next to each sidebar item (e.g., "Calculator (⌘1)")

Reuses the existing dialog/popover components from the UI library.

Scope

Good first issue — all components already exist.