fix(cli,tui): align CJK / wide-char markdown tables (#23863)

CJK and emoji glyphs render as two terminal cells but JS String#length
and the model's own padding count them as one, so any markdown table
with Chinese / Japanese / Korean cells drifts right per row when a
real terminal renders it. Both surfaces fix this with a display-cell
width measurement (wcswidth on the Python side, stringWidth on the
TUI side).

Changes:
- agent/markdown_tables.py: new helper. realign_markdown_tables(text)
  detects markdown table blocks (header + |---| divider) and
  rewrites the row padding using wcwidth.wcswidth so every pipe and
  dash lines up across rows. No-op on text without tables.
- cli.py: hook the helper into _render_final_assistant_content for
  strip / render modes (raw passes through untouched), and into the
  streaming line emitter so live token-by-token rendering also
  produces aligned tables. A small two-buffer state machine in
  _emit_stream_text holds table rows until the block ends, then
  flushes them through the realigner so all rows pad to a single
  per-column width.
- ui-tui/src/components/markdown.tsx: renderTable now uses
  stringWidth (Bun.stringWidth fast path + East-Asian-width-aware
  fallback, already memoised in @hermes/ink) instead of UTF-16
  String#length for both column-width measurement and per-cell
  padding. Drops the comment that documented the bug as a deliberate
  limitation.

Validation:
- New tests/agent/test_markdown_tables.py (11): every rebuilt block
  shares pipe column offsets across rows for pure CJK, mixed
  CJK+emoji, ragged-row, and multi-table inputs.
- Updated tests/cli/test_cli_markdown_rendering.py: the existing
  strip-mode test asserted exact whitespace; rewritten to assert the
  alignment contract (cell content survives + every rendered row
  shares pipe offsets).
- New ui-tui markdown.test.ts case (1): rendered column-2 start
  offset is identical for the header + every body row, including
  the CJK row that drifted before the fix.
- Live: hermes chat -q with the user-reported screenshot prompt now
  produces a perfectly aligned table on the wire (header, divider,
  4 body rows including '通义千问', all pipes at identical columns).

ui-tui/src/components/markdown.tsx

@@ -1,4 +1,4 @@
-import { Box, Link, Text } from '@hermes/ink'
+import { Box, Link, stringWidth, Text } from '@hermes/ink'
 import { Fragment, memo, type ReactNode, useMemo } from 'react'
 
 import { ensureEmojiPresentation } from '../lib/emoji.js'
@@ -170,16 +170,22 @@ export const stripInlineMarkup = (v: string) =>
     .replace(/\\\(([^\n]+?)\\\)/g, '$1')
 
 const renderTable = (k: number, rows: string[][], t: Theme) => {
-  const widths = rows[0]!.map((_, ci) => Math.max(...rows.map(r => stripInlineMarkup(r[ci] ?? '').length)))
+  // Column widths in *display cells*, not UTF-16 code units.  CJK
+  // glyphs and most emoji render as two cells but `String#length`
+  // counts them as one, which collapses Chinese / Japanese / Korean
+  // tables into drift across rows.  `stringWidth` (Bun.stringWidth
+  // fast path + an East-Asian-width-aware fallback, memoised in
+  // @hermes/ink) returns the actual cell count.
+  const cellWidth = (raw: string) => stringWidth(stripInlineMarkup(raw))
+
+  const widths = rows[0]!.map((_, ci) => Math.max(...rows.map(r => cellWidth(r[ci] ?? ''))))
 
   // Thin divider under the header.  Without it tables look like prose
   // with extra spacing because the header is just accent-coloured text
   // (#15534).  We avoid full borders on purpose — column widths come
-  // from `stripInlineMarkup(...).length` (UTF-16 code units, not
-  // display width), so a real outline often misaligns on emoji and
-  // East-Asian wide characters; one dim solid rule (`─`) under row 0
-  // plus tab-style column gaps reads cleanly on every terminal we
-  // tested.
+  // from `stringWidth(...)`, so the dividers and the row content stay
+  // in sync on CJK / emoji tables; tab-style column gaps still read
+  // cleanly without the boxed look.
   const sep = widths.map(w => '─'.repeat(Math.max(1, w))).join('  ')
 
   return (
@@ -190,7 +196,7 @@ const renderTable = (k: number, rows: string[][], t: Theme) => {
             {widths.map((w, ci) => (
               <Text bold={ri === 0} color={ri === 0 ? t.color.accent : undefined} key={ci}>
                 <MdInline t={t} text={row[ci] ?? ''} />
-                {' '.repeat(Math.max(0, w - stripInlineMarkup(row[ci] ?? '').length))}
+                {' '.repeat(Math.max(0, w - cellWidth(row[ci] ?? '')))}
                 {ci < widths.length - 1 ? '  ' : ''}
               </Text>
             ))}