feat: display keybindings in modal

[thecentinol]

Summary

Adds a new modal model that renders all application keybindings in a scrollable view using bubbles/help and bubbles/viewport.

Changes

• Modal Implementation: Built a dedicated keybindings modal model wrapping bubbles/viewport.
• Global Navigation & Keybindings:
  • Added a global Cancel (Esc) keybinding to close active modals (used for both password and keybinding modals).
  • Wired up ? hotkey and event handlers to open/close the modal from the root model.
  • Added filtering methods to Keybindings and a ToBubblesBatch helper for converting a slice of Binding to bubbles/key.Binding.
• Group Restructuring:
  • Split wifiGroup into separate Saved and Available groups for clearer visual organization.
  • Refactored tableGroup to represent generic navigation across UI models, and renamed it to navGroup.
• Styling: Defined theming under KeybindsModalTheme.

Result

Pressing ? anywhere (unless another modal is focused/active - i.e., error or password modal) in the app displays an viewport listing all keyboard shortcuts categorized by domain, allowing users to easily discover available keybindings.