[BUG] /agents view line-stacking persists with Nerd Fonts (Cascadia Code / CaskaydiaCove Nerd Font Mono) on Windows Terminal after #58579/#58487 fix

Splitting this out from #58579 (closed as completed, shipped in v2.1.143). That fix addressed the line-stacking/overlap in the /agents view for the default-font rendering path on Windows Terminal / PowerShell.

A separate report on that thread indicates the problem still reproduces — but only with Nerd Fonts — after the fix:

• Reported by @bijancamp on #58579 (comment), on v2.1.178, win32-x64, Windows Terminal.
• Occurs with both Cascadia Code and CaskaydiaCove Nerd Font Mono.
• Does not reproduce on the default profile font (v2.1.179, Windows 11 + Windows Terminal + PowerShell 7.6) per follow-up testing on the same thread.

Because it is font-specific, this looks like a distinct issue from the original #58579 / #58487 (which affected the default font path for all users). The likely culprit is a glyph-width / character-width miscalculation for the Private Use Area glyphs that Nerd Fonts add — the cell-width estimate disagrees with what the terminal actually renders, so columns drift and rows stack.

Repro (from the thread)

1. Windows Terminal with font set to Cascadia Code or CaskaydiaCove Nerd Font Mono.
2. Run claude and open the /agents view.
3. Rows stack / overlap.

Expected

/agents rows render cleanly regardless of the terminal font (or fall back to a safe width assumption for unknown glyphs).

Notes for triage

• A clean repro on the maintainer side would benefit from the exact wt --version and whether it happens with the stock PowerShell profile font vs. the Nerd Font, to confirm it's glyph-width-specific.
• Filing separately so the font-specific path isn't lost now that #58579 and #58487 are closed.