control panel: audio devices, icon font, padding, blur

- audio view: output/input device switching, master volume + mic, and
  per-application streams with their own sliders (pactl sink-inputs)
- icons rendered black because GTK used the desktop font (Noto Sans), which
  has no Nerd Font glyphs; Pango's per-glyph fallback then ignored the css
  colour. Icon classes now name the font explicitly.
- bspwm drew a focus border around the panel that fought the css rounded
  corners: border=off on the rule
- picom now blurs translucent surfaces, so the panel reads as glass rather
  than showing the text behind it
- padding and spacing throughout: frame 20px, section margins, card padding

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

.config/bspwm/picom.conf

@@ -68,3 +68,15 @@ fade-exclude = [
 animation-exclude = [
   "class_g = 'Rofi'",
 ];
+
+# Translucent surfaces over busy content read as noise without blur.
+blur-method = "dual_kawase";
+blur-strength = 6;
+blur-background = true;
+blur-background-frame = true;
+blur-background-exclude = [
+  # the particle layer is transparent on purpose; blurring it would smear
+  # the wallpaper behind it
+  "window_type = 'desktop'",
+  "class_g = 'Particles'",
+];