[FEAT]: Add Vim-Style Keybindings

[Irtesaam]

Description:

Introduce an optional Vim mode for users who prefer keyboard-driven workflows. This will allow advanced users to manage tasks and lists more efficiently without relying on mouse interactions.

Proposed Behavior:

Enable/Disable: Toggle Vim mode in extension settings (disabled by default for majority users).

Normal Mode (navigation / actions)

• n / N → Next / previous search result
• : → Enter command-line mode (for advanced list ops)
• j / k → Move down / up through tasks
• gg → Jump to first task
• G → Jump to last task
• dd → Delete current task
• x → Mark task as done (toggle)
• / → Search/filter tasks (prompt at bottom)

Insert Mode:

• Standard text input for typing task content
• Esc → Return to Normal mode (⚠️ must ensure this doesn’t conflict with closing the popup)