feat: consolidate Kanagawa theme and refine Walker and Limine styling

docs/constellation.md

@@ -25,6 +25,12 @@ use a flake to declare its tools without Nix owning the surrounding workspace.
 
 ## What that means so far
 
+- Themes are complete Nix modules, not just palettes. Select one through
+  `modules/capabilities/theme.nix`; it may install native theme plugins, configure
+  their behavior and choose assets for each application. Kanagawa is the first
+  implementation. Shared interaction/layout choices stay in capability modules.
+  Stylix is not selected: preserving theme-specific behavior matters more than
+  forcing applications through one generated color scheme.
 - Neovim, Niri, Walker and the terminal feel right: direct, keyboard-driven
   interaction with useful connections to the rest of the environment.
 - Use Handy for local plain dictation, mainly English with occasional Dutch.