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/btop/btop.conf

@@ -0,0 +1,15 @@
+color_theme = "sakura-line"
+theme_background = False
+truecolor = True
+vim_keys = False
+rounded_corners = True
+graph_symbol = "braille"
+shown_boxes = "cpu mem net proc"
+update_ms = 1000
+proc_sorting = "cpu lazy"
+proc_gradient = True
+cpu_graph_upper = "total"
+show_uptime = True
+temp_scale = "celsius"
+clock_format = "%H:%M"
+background_update = True