Add a command-mode shortcut to create a SQL cell below #10688

Description

Marimo command mode supports Esc, then b to create a new Python cell below the focused cell.
Creating a SQL cell requires an additional conversion step:

1. Esc
2. b
3. Cmd/Ctrl + Shift + L

It would be useful to have a command-mode shortcut such as Esc, then q that directly creates and focuses a new SQL cell below the current cell.

Hex supports this interaction pattern: in command mode, q creates a SQL cell. Its keyboard-shortcut documentation describes command mode and notes that its Add Cell menu exposes shortcuts for creating specific cell types.

Suggested solution

Add a configurable action such as command.createSQLCellAfter, with q as its default command-mode binding.

Expected behavior:

• Press Esc to enter command mode.
• Press q.
• Create a new SQL cell immediately below the selected cell.
• Focus the new SQL editor.
• Do not execute the currently selected cell.
• Continue using the existing default SQL engine and output settings.
• Expose the action in the keyboard-shortcut settings so users can remap it.
  The existing b shortcut should continue creating a regular Python cell.

Relationship to #6790

This is related to #6790, which proposes that Shift+Enter on a SQL cell should create another SQL cell.

A dedicated command-mode shortcut may be a better approach because it is explicit and does not change the existing semantics of Shift+Enter:

• It separates cell creation from cell execution.
• It works regardless of the current cell’s type.
• Users can deliberately choose between a Python cell with b and a SQL cell with q.
• It avoids implicitly deriving the new cell type from the preceding cell.
• It does not affect users who expect newly created cells to default to Python.

The two proposals could coexist, but the command-mode shortcut provides the workflow without changing existing behavior.

Are you willing to submit a PR? (You must receive approval from the team before submitting a PR.)

• Yes

Alternatives

No response

Additional context

No response