Rebuild Displays around the canvas, and let the transaction keep color

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

README.md

@@ -80,6 +80,21 @@ and remote desktop. The allow-list in
 [`services/SystemSettings.qml`](config/dot/quickshell/services/SystemSettings.qml)
 is what decides; anything not on it is a panel Panama owns itself.
 
+Displays is one of the panels it owns, and the only one where a wrong answer
+can leave you unable to see well enough to undo it. So every change there is
+applied as one complete layout, read back from the compositor, and reverted
+after fifteen seconds unless you keep it — resolution, scale, rotation,
+position and primary display, and now colour profile, bit depth, SDR
+brightness and saturation, and mirroring with them. Two of those opt out of
+part of that, for reasons rather than convenience. A per-display variable
+refresh rate override is applied but never verified, because `hyprctl` reports
+whether adaptive sync is live this instant rather than what was asked for. And
+a mirrored display's position is not asserted at all: the compositor stacks it
+on the display it mirrors and ignores the coordinates the rule carried, so
+holding it to them would make Keep permanently unavailable. Monitor brightness
+sits outside the transaction entirely — it is the panel's own backlight over
+DDC, and the buttons on the bezel change it behind our back.
+
 | Piece | What it is |
 |---|---|
 | `config/dot/hypr/` | Compositor config. **Lua, not hyprlang** — see its README |