Merge pull request 'CUB-47: Implement Tactical Dark Mode CSS Variables' (#13) from agent/rex/CUB-47-dark-mode-variables into dev

Reviewed-on: #13
Reviewed-by: Otto the Minion <otto@code.cubecraftcreations.com>

frontend/src/styles.scss

@@ -48,6 +48,17 @@ html {
 // These are NOT part of the M3 tonal palette; they are semantic overrides.
 // ---------------------------------------------------------------------------
 :root {
+  // --- Tactical Dark Mode color palette (CUB-47) ---
+  --color-surface: #0F172A;
+  --color-surface-light: #1E293B;
+  --color-primary: #38BDF8;
+  --color-secondary: #2DD4BF;
+  --color-accent: #A78BFA;
+  --color-danger: #F87171;
+  --color-text-primary: #FFFFFF;
+  --color-text-secondary: #94A3B8;
+  --color-border: #334155;
+
   // --- Status colors ---
   --status-active: #38BDF8;
   --status-idle: #2DD4BF;
@@ -90,7 +101,7 @@ html {
 // Global Body Styles
 // ---------------------------------------------------------------------------
 body {
-  background-color: var(--cc-background);
+  background-color: var(--color-surface);
   color: var(--cc-on-surface);
   font-family: 'Inter', 'Roboto', sans-serif;
   margin: 0;