control panel: fix css priority, drop blur, soften active tiles

The panel styled itself at PRIORITY_APPLICATION (600) while
~/.config/gtk-3.0/gtk.css loads at PRIORITY_USER (800) and styles plain
'button'. The user sheet won, so tile backgrounds never applied - but the
more specific '.tile.active .tile-icon { color: #0f0d17 }' did, which is why
icons rendered black on dark tiles. The panel now loads at USER + 1.

- global blur made every translucent window fuzzy, not just the panel: removed
- picom no longer re-rounds the panel; it clipped at 12px over an 18px css
  radius and chewed the corners
- active tiles are a tint plus an accent border rather than a solid accent fill
- 10px transparent gutter outside the card, 20px padding inside
- the particles tile was using a television glyph; now an atom

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

.config/bspwm/picom.conf

@@ -58,6 +58,9 @@ rounded-corners-exclude = [
   "window_type = 'dock'",
   # never round a fullscreen game
   "_NET_WM_STATE@:32a *= '_NET_WM_STATE_FULLSCREEN'",
+  # the control panel draws its own rounded card; picom clipping it at a
+  # different radius made the corners look chewed
+  "class_g = 'Control-panel.py'",
 ];
 
 # The control centre redraws by relaunching rofi, so the open/close zoom and
@@ -68,15 +71,3 @@ 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'",
-];