Add keyboard shortcuts for common actions

[Awaiswilll]

Description

Add keyboard shortcuts for common dweb OS actions to improve developer productivity.

Shortcuts to Add

Shortcut	Action
Ctrl+K	Open command palette / quick search
Ctrl+1	Go to Dashboard
Ctrl+2	Go to Browser
Ctrl+3	Go to AI Agent
Ctrl+4	Go to Domains
Ctrl+5	Go to Repositories
Ctrl+6	Go to Settings
Ctrl+Shift+R	Refresh services
Ctrl+/	Show keyboard shortcuts help

What Needs to Be Done

• Create keyboard shortcut hook (useKeyboardShortcuts)
• Register shortcuts in App.tsx
• Add shortcuts help modal (Ctrl+/)
• Document shortcuts in README

Acceptance Criteria

• All shortcuts work on Windows, Mac, and Linux
• Shortcuts don't conflict with browser shortcuts
• Help modal shows all available shortcuts
• Shortcuts are documented in README

Relevant Files

• src/App.tsx — Global shortcut registration
• src/components/Sidebar.tsx — Navigation shortcuts

[kavix]

Like to work with that issue. Can @Awaiswilll assign me?