feat: render new xhigh effort level with its own color

[FZ1010]

Closes #23.

Summary

Claude Code v2.1.111 added xhigh as an effort level between high and max (Opus 4.7 only). Both scripts fall through to the green default, so xhigh is indistinguishable from high.

This PR adds explicit high and xhigh cases to the effort switch in both statusline.sh and statusline.ps1. xhigh gets its own color so it's visually distinct from high (green) and max (red).

Color choice

I went with purple (#A78BFA, rgb(167, 139, 250)) for xhigh since green (high), red (max), orange (medium), and yellow (usage-50%) are already in the palette, and purple reads well on both dark and light terminals. Entirely a matter of taste — happy to change it to whatever you prefer (another shade, a different hue, a symbol prefix like !xhigh, etc.).

Verified

Both scripts tested locally with CLAUDE_CODE_EFFORT_LEVEL=xhigh against a mock Claude Code input. Output contains \033[38;2;167;139;250m (purple) for xhigh and the existing ANSI codes for the other levels.

level	color (before)	color (after)
low	dim	dim
medium	orange (abbrev. med)	orange (abbrev. med)
high	green (via default)	green (explicit)
xhigh	green (via default) ❌	purple (explicit) ✅
max	red	red

Test plan

• CLAUDE_CODE_EFFORT_LEVEL=xhigh bash statusline.sh < mock.json — emits purple
• CLAUDE_CODE_EFFORT_LEVEL=xhigh powershell -NoProfile -File statusline.ps1 < mock.json — emits purple
• Other levels (low, medium, high, max) unchanged
• Unknown values still hit the green default branch