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/cava/config

@@ -0,0 +1,32 @@
+# cava - Sakura Line
+# background = default keeps the terminal's transparency showing through.
+
+[general]
+framerate = 60
+autosens = 1
+overshoot = 20
+bar_width = 2
+bar_spacing = 1
+
+[input]
+method = pulse
+source = auto
+
+[output]
+method = ncurses
+channels = stereo
+mono_option = average
+
+[smoothing]
+noise_reduction = 45
+
+[color]
+background = default
+gradient = 1
+gradient_count = 6
+gradient_color_1 = '#7c9ede'
+gradient_color_2 = '#92b9ea'
+gradient_color_3 = '#a3c0cb'
+gradient_color_4 = '#d0a4d8'
+gradient_color_5 = '#e0798f'
+gradient_color_6 = '#e9c79b'