fix: pad description box rows by display width

[NoirVoider]

Description

truncateMultilineText() padded each wrapped row with String#padEnd, which counts UTF-16 code units, while renderBox() draws the description box border assuming the row occupies exactly width terminal columns. Descriptions containing characters whose display width differs from their code-unit length (CJK, BMP-wide emoji such as U+2B50, ZWJ emoji sequences) therefore produced a misaligned right border.

This reuses the display-width helper that already exists in the same file and is already used by truncateText(), so both boxes pad by display width. ASCII descriptions are unaffected (wcswidth(text) === text.length).

Fixes #477

Before / after (width = 28, i.e. descriptionWidth - borderWidth)

sample	code units	display cells	before (padEnd)	after (wcPadEnd)
Run OpenCode with a message	27	27	28 ✓	28 ✓
以一条消息运行 OpenCode	16	23	35 ✗	28 ✓
⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐ (U+2B50)	10	20	38 ✗	28 ✓
🚀🚀🚀🚀🚀🚀🚀🚀 (U+1F680)	16	16	28 ✓	28 ✓
👨‍👩‍👧👨‍👩‍👧👨‍👩‍👧	24	18	22 ✗	28 ✓

Tests

Added a truncateMultilineText suite to src/tests/utils/ui.test.ts:

• ASCII rows keep the previous padding (regression guard)
• CJK / BMP emoji / astral emoji / ZWJ rows are padded to the requested display width
• renderBox(truncateMultilineText(...), width + 2) lines are exactly width + 2 columns
• maxHeight truncation still marks the last line with …

3 of the new assertions fail on main, pass with the fix:

✕ pads wide characters by display width, not by code units
✕ pads emoji by display width
✕ keeps box borders aligned for wide characters
Tests: 3 failed, 7 passed, 10 total

Full suite with the fix:

Test Suites: 1 skipped, 14 passed, 14 of 15 total
Tests:       10 skipped, 208 passed, 218 total
Snapshots:   93 passed, 93 total

[NoirVoider]

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