fix(ui): drop the border from the screen root

The root fills the whole panel, so a border sent it through the per-pixel
roundRect path on every draw. The panel background is not a card; cards
that want a border set one explicitly.

lua/lib/ui.lua

@@ -79,7 +79,6 @@ local function palette(seed)
     pressedFace = color(accent),
     pressedColor = color(background),
     focusColor = color(accent),
-    focusWidth = 2,
     radius = seed.radius,
   }
 end
@@ -133,7 +132,7 @@ end)
 
 local STYLE_KEYS = {
   "color", "fill", "border", "face", "pressedFace", "pressedColor",
-  "focusColor", "focusWidth", "radius", "font", "textStyle",
+  "focusColor", "radius", "font", "textStyle",
 }
 
 local function applyStyle(id, spec)
@@ -301,15 +300,15 @@ local Screen = {}
 Screen.__index = Screen
 
 applyPalette = function(root)
+  -- The root is the panel background, not a card: no border, so it takes the fast fillRect
+  -- path rather than the per-pixel roundRect one. Radius stays so cards inherit it.
   node.setStyle(root, {
     color = ui.theme.color,
     background = ui.theme.background,
-    border = ui.theme.muted,
     face = ui.theme.face,
     pressedFace = ui.theme.pressedFace,
     pressedColor = ui.theme.pressedColor,
     focusColor = ui.theme.focusColor,
-    focusWidth = ui.theme.focusWidth,
     radius = ui.theme.radius,
     font = gui.FONT_UI,
   })