Add an inward glow bleeding from the border over the window

New plugin:hyprchrome:glow_size (px, 0 = off) and glow_strength (0-1)
bleed the border's own gradient inward past the window edge, over the
window's own pixels. Off by default, so existing setups are unchanged.

Drawn into the hole the ring's even-odd fill already leaves behind, from
overlapping layers - one per px of depth - each covering the window edge
inward to a progressively greater depth. Overlapping rather than abutting
disjoint bands avoids an antialiasing seam at every shared edge; the cost
is that a layer composites over every deeper one, so its alpha is solved
outermost-inward from the target profile rather than being it.

That profile is strength * (1 - d/glow)^2.2: steep off the window edge,
easing into a tail that reaches zero tangentially so there's no ring
where it stops.

Corner handling, in order of how much it mattered:
- Each layer's outer edge is the ring's inner boundary verbatim, chamfer
  vertices and all. Anything else detaches the glow from the frame and
  opens a sliver of unpainted window at each corner.
- Each layer's inner edge - which is what the falloff's contours actually
  follow - is filleted in proportion to its own depth, so the glow reads
  as chamfered where it meets the frame and rounder as it fades inward.
- Those inner edges also shrink their chamfer by (2-sqrt2) per px of
  inset. Insetting a chamfered rect while holding the chamfer constant
  moves the 45-degree face in by d*sqrt(2) rather than d, which had the
  glow running ~41% deeper at every corner than along the sides.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ChromeConfig.hpp

@@ -18,6 +18,14 @@ struct ChromeConfig {
   SP<GradientValue> activeColor;
   SP<GradientValue> inactiveColor;
 
+  // How far the border's glow bleeds inward past the window edge, over the
+  // window's own pixels, in logical pixels. 0 disables the glow entirely.
+  SP<IntValue> glowSize;
+
+  // Peak opacity of that glow, at the window edge, as a fraction of the
+  // border color's own alpha.
+  SP<FloatValue> glowStrength;
+
   // Height of the title bar hanging off the floating top-border cutout, in
   // logical pixels.
   SP<IntValue> titlebarHeight;