feat: ctrl+T opens omnibox in a new tab or split/floating/stacked pane

[bnema]

Summary

Currently, pressing ctrl+T has no defined behavior for opening the omnibox in a new context. This issue proposes binding ctrl+T to open the omnibox and let the user decide (or configure) where the new page should land.

Desired behavior

When ctrl+T is pressed, the omnibox opens and the resulting navigation target opens in one of the following modes (user-selectable or configurable):

• New empty tab — classic browser behavior, a blank tab with the omnibox focused
• Stacked pane — opens as a new pane stacked vertically in the current layout
• Split pane — opens as a horizontal split alongside the current view
• Floating pane — opens as a floating overlay, useful in tiling WM workflows

Motivation

Dumber targets tiling WM users who expect flexible, keyboard-driven navigation. A single ctrl+T shortcut that integrates with the existing pane/layout system would make opening new content feel native to that workflow, rather than forcing a context switch to reach the omnibox.

Acceptance criteria

• ctrl+T focuses the omnibox (reusing the existing omnibox component)
• The navigation result opens in a new empty tab by default
• At least one of stacked / split / floating pane modes is supported
• The target mode can be triggered by a modifier key combo or a config option (e.g. ctrl+shift+T for split)
• Behavior is documented in keybindings reference