Sakura Line: retheme the whole desktop from the wallpaper

Palette sampled from bspwm/wallpaper/wallpaper.jpg and applied per-role
(not per-hex, so terminal green stays green and nvim's LineNr/Comment
stay recessive) across st, kitty, polybar, rofi, dunst, nvim, qt5ct/qt6ct
and GTK 2/3/4.

Also:
- rofi drun centred, icons enabled
- polybar translucent (true ARGB) and rounded; picom corner-radius, with
  the desktop layer and fullscreen windows excluded
- fix qt5ct color_scheme_path pointing at a nonexistent /home/carrie
- export QT_QPA_PLATFORMTHEME so qt6ct is actually consulted
- point GTK at an icon theme that exists on this system
- add .config/rice: one-shot install.sh (--dry-run supported), package
  list, vendored st config.h (gitignored upstream) and the particles
  wallpaper-layer source, so a clone reproduces the rice

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Cn3dHfbgNYdbZvzb1b3GQt

.config/bspwm/picom.conf

@@ -46,3 +46,16 @@ shadow = false;
  detect-client-opacity = true;
  use-damage = true;
  log-level = "warn";
+
+# --- rounded corners ---
+corner-radius = 12;
+round-borders = 1;
+rounded-corners-exclude = [
+  # the particles layer is a full-screen desktop window; clipping it would
+  # notch the corners of the field
+  "window_type = 'desktop'",
+  # polybar rounds its own background
+  "window_type = 'dock'",
+  # never round a fullscreen game
+  "_NET_WM_STATE@:32a *= '_NET_WM_STATE_FULLSCREEN'",
+];