feat: consolidate Kanagawa theme and refine Walker and Limine styling

docs/constellation-work.md

@@ -118,6 +118,26 @@ reports are not a fresh comparison with this baseline.
 
 ## Open choices and next discussion
 
+Current focus: look and feel/theming, informed by `~/sync/notes/setup-todo.md`.
+The user accepted complete Nix theme modules with arbitrary plugin/configuration
+behavior, rather than Stylix or a palette-only abstraction. The single import in
+`modules/capabilities/theme.nix` selects `./_themes/kanagawa.nix`. `_themes` is
+excluded from automatic module discovery, so unselected themes are not loaded.
+Kanagawa owns GTK/icons/cursor, Qt integration, Kitty, Niri colors, Noctalia
+palette/font/wallpaper, Herdr colors, the native Neovim plugin and its setup, and
+Limine/SDDM/Plymouth appearance. Only Kanagawa is implemented so far; switching
+means selecting another module and rebuilding, not a live theme picker.
+Walker shares a compact layout with theme-provided colors: reduced padding,
+24px icons, clearer secondary text, and a smaller minimum window height.
+Limine's terminal background is fully transparent with no edge gradient so it
+does not obscure the wallpaper. Runtime appearance needs user verification.
+SDDM's purple-leaves theme and Plymouth's spinner are retained within Kanagawa;
+their visual redesign and the low-frame-rate boot animation remain open.
+Verification: flake evaluation and both workstation builds passed. A headless
+check of the built Neovim confirmed Kanagawa Wave, inactive-window dimming and
+the custom gutter setting. Rendered Herdr TOML, Walker XML and Limine settings
+also passed targeted checks. No system activation or live desktop changes performed.
+
 Dictation: plain local transcription is selected; rambling cleanup is deferred.
 Handy preferences are application-owned again: the Nix settings generator and
 startup reset are removed. The existing settings file is left untouched.
@@ -158,7 +178,7 @@ Niri workspace grouping stays informal while the user discovers what fits; Herdr
 provides enough structure for now. No workspace rules or fixed layout are needed.
 Further Herdr configuration, agent workflows and project management are explicitly
 deferred at the user's request. Do not use them as the default next task or request
-workflow feedback unless the user reopens the topic. The next area is not selected.
+workflow feedback unless the user reopens the topic. The active area is theming.
 Agent evaluation is
 explicitly deferred. Do not resume replacement-tool comparisons or ask for an
 evaluation task/budget as a prerequisite for this work.

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.