Bump libghostty and use upstream color parser

[emil-e]

Summary

• Bump the pinned ghostty-org/ghostty dependency from 07d3166 to c41c6b8.
• Handle upstream's new print_slice stream action in the comint filter so printable text is not dropped.
• Replace ghostel's local #RRGGBB parser with gt.color.RGB.parse where possible.

Verification

• zig build --prefix .
• zig build --prefix . -Doptimize=ReleaseFast
• bench/run-bench.sh --no-vterm --no-eat --no-term
• 5 interleaved longer A/B runs of backend/plain/native with --min-duration 3

Benchmark summary

Compared against 4c6351f (parent before this branch's two commits). Both sides were rebuilt with zig build --prefix . -Doptimize=ReleaseFast.

Section	Geomean speedup	Change
e2e	1.66x	+65.8%
backend	1.04x	+4.0%
stream	1.55x	+54.8%
tui-frame	1.48x	+48.2%
tui-partial	1.03x	+3.2%
engine	2.53x	+153.2%
overall	1.60x	+60.0%

Selected results:

Scenario	Before ms	After ms	Speedup
e2e/plain/ghostel	9.70	4.56	2.13x
e2e/urls/ghostel	18.29	14.13	1.29x
stream/ghostel-incr	14.88	9.38	1.59x
engine/plain/ghostel-incr/24x80	6.47	1.38	4.68x
engine/unicode/ghostel-incr/24x80	4.81	1.54	3.12x

The one reproducible regression is isolated to native PTY plain output:

Metric (backend/plain/native)	Before	After	Change
Mean over 5 longer interleaved runs	17.25 ms	19.24 ms	0.90x (-10.3%)
Median	17.33 ms	19.31 ms	0.90x (-10.2%)
Stddev	0.15 ms	0.17 ms	—

This likely indicates the faster VT engine has moved the bottleneck to the native PTY read/event-notification path: plain parsing no longer provides as much incidental batching before WouldBlock, so the reader may notify/redraw more often. Parser-only and stream-only paths show large wins, so this does not look like a raw VT parsing regression.