docs: update README and DECISIONS for Walker moonarch theme

DECISIONS.md

@@ -1,5 +1,11 @@
 # Decisions
 
+## 2026-04-07 – Walker theme: gtk-inherit → moonarch with fixed colors
+- **Who**: Dominik, ClaudeCode
+- **Why**: gtk-inherit theme relied on GTK4 color inheritance which works but doesn't update live when switching GTK themes (Walker service needs restart). Explicit color definitions make the theme self-contained and predictable.
+- **Tradeoffs**: Colors no longer auto-follow GTK theme changes. Acceptable since moonarch uses a fixed Catppuccin Mocha palette anyway.
+- **How**: Renamed theme to moonarch, added @define-color with Colloid-Grey-Dark-Catppuccin values, reduced border/shadow weight.
+
 ## 2026-04-07 – Migrate archinstall config to v4 format
 - **Who**: Dominik, ClaudeCode
 - **Why**: archinstall v4.1 introduced new canonical key names. Old keys (audio_config, bootloader, custom-commands) are soft-deprecated and auto-mapped, but custom-commands (hyphen) vs custom_commands (underscore) was risky.

README.md

@@ -112,7 +112,7 @@ defaults/
   xdg/                          System-wide XDG configs (deployed to /etc/xdg/)
     niri/config.kdl               Compositor: layout, keybinds, startup apps
     waybar/config, style.css      Bar: modules, layout, Catppuccin styling
-    walker/config.toml, themes/   Launcher: Walker config + gtk-inherit theme
+    walker/config.toml, themes/   Launcher: Walker config + moonarch theme (Catppuccin Mocha)
     foot/foot.ini                 Terminal: font, colors, keybinds
     swaync/config.json, style.css Notifications: appearance, behavior, MPRIS
     kanshi/config                 Display profiles (empty seed, user-configured via wdisplays)