fix: scroll command-bar suggestions by display width so wide characters stay visible

[greymoth-jp]

The autocomplete suggestion strip in the info bar can scroll to the wrong offset when a suggestion contains full-width characters (CJK ideographs, kana, full-width forms), leaving the selected suggestion partly or fully off screen.

scrollToSuggestion tracks its column position with util.CharacterCountInString, which counts characters, so a CJK ideograph counts as 1. The strip itself is drawn by display width: Display advances by runewidth.RuneWidth per rune, and totalSize already sums runewidth.StringWidth(n). Once a suggestion is wider than its character count, the scroll math and the renderer disagree.

Example: suggestions ["日本語テスト", "ok", "end"] with the second one selected, in a 14-column strip. 日本語テスト is 6 characters but 12 display columns, so the renderer draws ok at columns 13 to 15. scrollToSuggestion places it at column 7, keeps hscroll at 0, and ok is clipped at the right edge. Measuring by display width sets hscroll to 2 and ok is fully visible.

Switching that line to runewidth.StringWidth(n) matches totalSize and the renderer. ASCII-only suggestions are unchanged, since there character count equals display width.

I confirmed the package builds and the internal/util tests pass. internal/display has no test files, so I checked the scroll offset against the renderer's true columns for the case above: wrong before, correct after, and unchanged for ASCII input.