fix(themes): light mode — the window glow tightens to a few px

The shadow color is the palette mantle: near-black on dark themes (a
normal ambient shadow) but a light warm tone on light ones, where the
20px range reads as a wide glow that bleeds into neighbouring windows
and the bar (hardware report, kiln-clay, 2026-07-18). Light mode now
defaults the range to 5px — the glow stays as an identity feature,
just tight; dark themes keep the soft 20px shadow. Still lib.mkDefault,
so downstream overrides keep working.

Verified V1 (generation renders range=5 under kiln-clay); on-hardware
before/after of the live desktop taken in the reporting session.

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

modules/home/hyprland.nix

@@ -1060,7 +1060,12 @@ in
         };
         shadow = {
           enabled = t.ui.shadow;
-          range = lib.mkDefault 20;
+          # The mantle-tinted shadow reads as a dark halo on dark themes
+          # but as a warm *glow* on light ones (mantle is light there) —
+          # kept as an identity feature, just tight (a few px) so it never
+          # bleeds into neighbouring windows or the bar (hardware report
+          # 2026-07-18); dark themes keep the soft 20px ambient shadow.
+          range = lib.mkDefault (if t.mode == "light" then 5 else 20);
           render_power = lib.mkDefault 3;
           color = rgba c.mantle "aa";
         };