Make copy line up/down shortcuts editable

[kallal79]

This updates the CodeMirror keymap override path so both commands use marimo hotkey config instead of fixed defaults, and adds a regression test to confirm custom overrides are applied.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Apr 16, 2026 8:01pm

[github-actions]

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[Copilot]

Pull request overview

This PR makes CodeMirror’s “copy line up/down” shortcuts configurable through marimo’s hotkey system (instead of being fixed), and adds a regression test to ensure overrides are respected.

Changes:

• Marked cell.copyLineUp / cell.copyLineDown as editable by removing editable: false from default hotkey definitions.
• Updated CodeMirror keymap overrides to (1) remove the built-in bindings for copy line up/down and (2) re-add them using HotkeyProvider values.
• Added a unit test confirming custom hotkey overrides are applied for these commands.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
frontend/src/core/hotkeys/hotkeys.ts	Allows “copy line up/down” to be user-editable by default.
frontend/src/core/codemirror/keymaps/keymaps.ts	Ensures CodeMirror uses marimo hotkey config for copy line up/down by overriding and rebinding these commands.
frontend/src/core/codemirror/keymaps/__tests__/keymaps.test.ts	Adds regression coverage verifying the override keymap uses provider-defined keys for the copy line commands.

[kallal79]

I have read the CLA Document and I hereby sign the CLA

[Light2Dark]

@kallal79 , could you have a look at fixing the type errors?