feat: rename Walker theme to moonarch, add explicit Catppuccin colors

Rename gtk-inherit theme to moonarch with fixed Colloid-Grey-Dark-
Catppuccin color definitions. Reduces border brightness and shadow
weight for a subtler appearance.

Closes #3

defaults/xdg/walker/config.toml

@@ -7,7 +7,7 @@ click_to_close = true
 as_window = false
 single_click_activation = true
 selection_wrap = false
-theme = "gtk-inherit"
+theme = "moonarch"
 disable_mouse = false
 page_jump_items = 10
 hide_quick_activation = false

defaults/xdg/walker/themes/moonarch/style.css

@@ -1,5 +1,10 @@
-/* ABOUTME: Walker theme that inherits colors from the active GTK4 theme.
-   ABOUTME: Only overrides layout/spacing — colors come from Colloid-Dark-Catppuccin or whatever is active. */
+@define-color window_bg_color #292c3c;
+@define-color window_fg_color #eff1f5;
+@define-color accent_bg_color #ccd0da;
+@define-color accent_fg_color rgba(17, 17, 27, 0.87);
+@define-color error_bg_color #ea999c;
+@define-color error_fg_color rgba(17, 17, 27, 0.87);
+@define-color theme_fg_color @window_fg_color;
 
 * {
   all: unset;
@@ -8,7 +13,7 @@
 
 popover {
   background: lighter(@window_bg_color);
-  border: 1px solid darker(@accent_bg_color);
+  border: 1px solid alpha(@accent_bg_color, 0.15);
   border-radius: 18px;
   padding: 10px;
 }
@@ -27,12 +32,12 @@ scrollbar {
 
 .box-wrapper {
   box-shadow:
-    0 19px 38px rgba(0, 0, 0, 0.3),
-    0 15px 12px rgba(0, 0, 0, 0.22);
+    0 19px 38px rgba(0, 0, 0, 0.15),
+    0 15px 12px rgba(0, 0, 0, 0.1);
   background: @window_bg_color;
   padding: 20px;
   border-radius: 20px;
-  border: 1px solid darker(@accent_bg_color);
+  border: 1px solid alpha(@accent_bg_color, 0.15);
 }
 
 .preview-box,