fix(editor): Count wide characters as two columns in column editing (#172)

Column-based editing computed columns with countColumn / findColumn, which count every grapheme as one column, and up/down and Clone Caret moved by pixel x, so block selections and cloned carets drifted on lines with CJK, fullwidth punctuation, Hangul, kana or emoji. A shared visible-column helper (UI side only, UTF-16 offsets in and out) now counts East Asian wide/fullwidth characters and emoji (ZWJ sequences, modifiers, flags, VS16) as 2, combining marks and format characters as 0, and expands tabs to the next tab stop.

It drives Alt+drag block selection, drag and Shift+arrows in Column Selection Mode, middle-drag block selection (new; not on Linux, where middle-click pastes the primary selection), the up/down goal column (kept across short lines; soft-wrapped and folded lines still move visually), Clone Caret Above/Below, the caret move after Comment Line, Tab padding to the next indent stop, and macro playback of arrow keys.

Claude-Session: https://claude.ai/code/session_01Dq6jQQn8ZhRfkkyj3PRutA

src/editor/core/cm/baseKeymap.ts

@@ -3,11 +3,14 @@
  * Those keys belong to IDE actions instead (keymaps in `platform/keymaps/`):
  * ⌘/Ctrl+Enter is Split Line, Ctrl+M / ⌃L Scroll to Center, Ctrl+[ / ] code
  * block navigation, ⌥⌘↑↓ / Ctrl+Alt+↑↓ Previous / Next Occurrence.
+ * Line up / down (with ⇧ too) keep the caret's visible column (`verticalMotion`).
  */
-import type { KeyBinding } from "@codemirror/view";
+import type { Command, KeyBinding } from "@codemirror/view";
 import {
   addCursorAbove,
   addCursorBelow,
+  cursorLineDown as cmCursorLineDown,
+  cursorLineUp as cmCursorLineUp,
   defaultKeymap,
   historyKeymap,
   indentLess,
@@ -15,8 +18,11 @@ import {
   insertBlankLine,
   redo,
   selectLine,
+  selectLineDown as cmSelectLineDown,
+  selectLineUp as cmSelectLineUp,
   toggleTabFocusMode,
 } from "@codemirror/commands";
+import { cursorLineDown, cursorLineUp, selectLineDown, selectLineUp } from "./verticalMotion";
 
 const DROPPED = new Set<unknown>([
   insertBlankLine, // Mod-Enter
@@ -28,8 +34,20 @@ const DROPPED = new Set<unknown>([
   indentMore, // Mod-]
 ]);
 
+const VERTICAL = new Map<Command | undefined, Command>([
+  [cmCursorLineUp, cursorLineUp],
+  [cmCursorLineDown, cursorLineDown],
+  [cmSelectLineUp, selectLineUp],
+  [cmSelectLineDown, selectLineDown],
+]);
+
+const vertical = (b: KeyBinding): KeyBinding =>
+  VERTICAL.has(b.run) || VERTICAL.has(b.shift)
+    ? { ...b, run: VERTICAL.get(b.run) ?? b.run, shift: VERTICAL.get(b.shift) ?? b.shift }
+    : b;
+
 export const editorBaseKeymap: readonly KeyBinding[] = [
-  ...defaultKeymap.filter((b) => !DROPPED.has(b.run)),
+  ...defaultKeymap.filter((b) => !DROPPED.has(b.run)).map(vertical),
   ...historyKeymap,
   // IDEA's Windows Redo is Ctrl+Shift+Z (Ctrl+Y is Delete Line); CodeMirror only binds it on macOS and Linux.
   { win: "Ctrl-Shift-z", run: redo, preventDefault: true },