style: mystical dark palette — deeper bg + purple chart colors

- Body/card backgrounds tinted deep purple (#120918 / #1e1330)
  instead of sterile gray-blue
- Chart colors: fuchsia+cyan for performance, violet+amber for
  network, layered purples for the players donut

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

rcon.css

@@ -1,12 +1,12 @@
 @import url(https://fonts.googleapis.com/css?family=Roboto:400,700);
 
 :root {
-  --rcon-bg: #252830;
+  --rcon-bg: #120918;
   --rcon-text: #cfd2da;
   --rcon-accent: #8b5cf6;
-  --rcon-card-bg: #434857;
+  --rcon-card-bg: #1e1330;
   /* Override BS5 dark theme body background */
-  --bs-body-bg: #252830;
+  --bs-body-bg: #120918;
 }
 
 body {