* Honor Ghostty background-opacity across all cmux chrome
Parse background-opacity from Ghostty config and propagate it through
the entire chrome pipeline: bonsplit tab bar (via RRGGBBAA hex),
browser panel/omnibar, titlebar, empty panel, and window background.
Decouple glass effect from sidebar blend mode — bgGlassEnabled now
defaults to false so opacity works independently. Add
GhosttyBackgroundTheme helper for consistent color+opacity resolution
across all UI surfaces.
Fixes https://github.com/manaflow-ai/cmux/issues/263
* Titlebar and chrome opacity matches terminal background-opacity
Use CALayer-level opacity for the titlebar background instead of SwiftUI
Color alpha, matching the terminal's Metal compositing path. Account for
the double alpha stacking in the terminal area (Bonsplit container bg +
Ghostty renderer) so the titlebar visually matches.
Also fix opacity-only config changes not triggering titlebar refresh on
Cmd+Shift+, reload.
bc1b6fd9eb