fix(ui): wrap agent note text by terminal cells

[kataokatsuki]

Summary

Plain-text agent notes (inline cards, hover popovers, static pager
inline-note lines) wrap their text with wrapText, which measures with
String#length and splits with String#slice — UTF-16 code units. The
renderers then clamp each line by terminal cells (fitText / padText),
so for CJK text (1 code unit = 2 cells) the wrapped lines come out up to
2× the box width and the clamp truncates them, silently dropping text.
Code-unit splitting can also cut an emoji's surrogate pair in half
(renders as U+FFFD).

• measure words with measureTextWidth and track the current line's
  cell width alongside the string, so line-fit checks compare cells to
  cells
• hard-split over-wide words with sliceTextByWidth, which walks
  grapheme clusters — wide characters and emoji are never split
• when the width is narrower than a single cluster, keep the remainder
  on one line for the renderer's fitText to clamp instead of dropping
  it, and decide "line is empty" by string length so zero-width
  characters can't produce over-wide lines
• add regression tests: CJK wrapping, mixed EN/JA text, odd widths,
  degenerate width 1, surrogate-pair and ZWJ emoji

Closes #566

Repro

With a 40-cell box and a 62-char / 124-cell Japanese summary:

	wrapText output
Before	2 lines of 40 code units = 80 cells each; the renderer clips both lines, silently dropping ~half the text
After	4 lines of ≤ 40 cells; nothing dropped

English output is unchanged — wrapping of ASCII input is byte-identical
before and after.

Testing

All run in a clean Linux container (oven/bun + git), matching CI's
ubuntu-latest environment:

• bun run typecheck
• bun run lint
• bun run format:check
• bun test src — 1,140 tests, 0 fail
• bun run test:tty-smoke — 9 pass, identical to a baseline run without
  this change (the harness needs util-linux script, which macOS lacks)

[greptile-apps]

PR author is not in the allowed authors list.

[kataokatsuki]

Thanks for the quick merge!