Dashboard: Add keyboard shortcuts (Cmd+K search, Cmd+N new memory)

[KD-K2N2]

Description

Add keyboard shortcuts to the Next.js dashboard for power users.

Shortcuts

Shortcut	Action
Cmd+K / Ctrl+K	Focus search
Cmd+N / Ctrl+N	Open new memory dialog
Escape	Close modals/panels
?	Show shortcuts help

Implementation

• Add a global useEffect with keydown listener in layout.tsx
• Use event.metaKey (Mac) or event.ctrlKey (Windows/Linux)
• Navigate to /search on Cmd+K
• Show a help modal on ?

Good first issue

Fun React feature. Dashboard is in packages/dashboard/src/.