[Feature] Implement Keyboard Shortcuts Architecture

[bigtcze]

Impact on UX:
Power users currently lack efficient keyboard navigation. Implementing standard hotkeys (Gmail/Notion style) significantly improves speed and accessibility.

Solution:
Leverage @mantine/hooks/useHotkeys to implement a consistent shortcut system.

1. Global Navigation (Layout.jsx):

• /: Focus Search.
• c: Focus 'Take a note...' input (when not editing).
• Ctrl/Cmd + k: Focus Search.

2. Note Editing (NoteModal.jsx):

• Ctrl/Cmd + s: Save (and maybe close).
• Ctrl/Cmd + Enter: Save & Close.
• Esc: Close Modal (Verify default behavior).

3. Checklist Management:

• Ensure Enter adds items and Backspace on empty items removes them.
• Arrow keys for navigation between items.

4. Documentation:

• Add a section in Settings or a keyboard shortcut help modal (?).

Tech Stack: Use Mantine's useHotkeys for cross-platform compatibility.

Complexity: 5