fix(hotkeys): make copy line up/down hotkeys editable

Copy line(s) up/down were listed in the Keyboard Shortcuts panel but
marked `editable: false`, because they were served by CodeMirror's
built-in `defaultKeymap` and so never consulted marimo's hotkey config.

Route both commands through the existing override mechanism already used
by `toggleComment`/`toggleBlockComment`: add them to OVERRIDDEN_COMMANDS
so the hardcoded bindings are filtered out of the default keymap, then
re-bind them in `overrideKeymap` using the configured hotkey. Default
keybindings are unchanged.

Closes #7056

Author: Abdulrehman-PIAIC80387

frontend/src/core/codemirror/keymaps/__tests__/keymaps.test.ts

@@ -1,8 +1,15 @@
 /* Copyright 2026 Marimo. All rights reserved. */
 
-import { defaultKeymap as originalDefaultKeymap } from "@codemirror/commands";
+import {
+  copyLineDown,
+  copyLineUp,
+  defaultKeymap as originalDefaultKeymap,
+} from "@codemirror/commands";
 import { describe, expect, it } from "vitest";
-import { HotkeyProvider } from "@/core/hotkeys/hotkeys";
+import {
+  HotkeyProvider,
+  OverridingHotkeyProvider,
+} from "@/core/hotkeys/hotkeys";
 import { visibleForTesting } from "../keymaps";
 
 const { defaultKeymap, defaultVimKeymap, overrideKeymap, OVERRIDDEN_COMMANDS } =
@@ -40,4 +47,26 @@ describe("keymaps", () => {
       expect(keys.some((k) => k.run === command)).toBe(true);
     }
   });
+
+  it.each([
+    ["cell.copyLineUp", copyLineUp, "Alt-Shift-ArrowUp"],
+    ["cell.copyLineDown", copyLineDown, "Alt-Shift-ArrowDown"],
+  ] as const)(
+    "%s is bound to the configured hotkey, not CodeMirror's default",
+    (action, command, defaultKey) => {
+      // Without an override, the binding matches CodeMirror's default key.
+      expect(
+        overrideKeymap(HotkeyProvider.create()).find((k) => k.run === command)
+          ?.key,
+      ).toBe(defaultKey);
+
+      // With an override, the binding follows the user's configured key.
+      // This is what `editable: true` on these hotkeys promises.
+      expect(
+        overrideKeymap(
+          new OverridingHotkeyProvider({ [action]: "Ctrl-d" }),
+        ).find((k) => k.run === command)?.key,
+      ).toBe("Ctrl-d");
+    },
+  );
 });

frontend/src/core/codemirror/keymaps/keymaps.ts

@@ -1,6 +1,8 @@
 /* Copyright 2026 Marimo. All rights reserved. */
 
 import {
+  copyLineDown,
+  copyLineUp,
   cursorCharLeft,
   cursorCharRight,
   cursorLineDown,
@@ -94,6 +96,8 @@ export function keymapBundle(
 const OVERRIDDEN_COMMANDS = new Set<Command | undefined>([
   toggleComment,
   toggleBlockComment,
+  copyLineUp,
+  copyLineDown,
 ]);
 
 const defaultKeymap = once(() => {
@@ -111,6 +115,14 @@ const overrideKeymap = (keymap: HotkeyProvider): readonly KeyBinding[] => {
       key: keymap.getHotkey("cell.toggleBlockComment").key,
       run: toggleBlockComment,
     },
+    {
+      key: keymap.getHotkey("cell.copyLineUp").key,
+      run: copyLineUp,
+    },
+    {
+      key: keymap.getHotkey("cell.copyLineDown").key,
+      run: copyLineDown,
+    },
   ];
 };
 

frontend/src/core/hotkeys/hotkeys.ts

@@ -256,13 +256,11 @@ const DEFAULT_HOT_KEY = {
     name: "Copy line(s) up",
     group: "Editing",
     key: "Alt-Shift-ArrowUp",
-    editable: false,
   },
   "cell.copyLineDown": {
     name: "Copy line(s) down",
     group: "Editing",
     key: "Alt-Shift-ArrowDown",
-    editable: false,
   },
 
   // Markdown