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/particles.conf

@@ -0,0 +1,28 @@
+# particles - wallpaper layer
+# Tuned for bspwm/wallpaper/wallpaper.jpg: a bright, busy image, so the field
+# is white and fairly opaque. Preview any change without touching the desktop:
+#   particles --snapshot /tmp/p.png --snapshot-bg ~/.config/bspwm/wallpaper/wallpaper.png
+# Reload a running instance after editing:  pkill -HUP particles
+
+density        = 55
+radius         = 2.4
+glow           = 4.0
+opacity        = 1.0
+color          = ffffff
+
+link-distance  = 140
+link-width     = 1.6
+link-opacity   = 0.85
+link-color     = ffffff
+
+speed          = 24
+edges          = bounce
+
+cursor           = grab,repel
+cursor-distance  = 180
+cursor-strength  = 1.0
+cursor-response  = 9
+
+fps                = 60
+keep-below         = true
+pause-when-covered = true