feat: interfaz clara unificada en Centro de Mando

Shell con nav agrupada y activa, PageHeader común, tipografía y tokens.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/app/globals.css

@@ -3,13 +3,43 @@
 @tailwind utilities;
 
 :root {
-  --background: #0B0F19;
-  --foreground: #F3F4F6;
-  --border: #1F2937;
+  --background: #0b0f19;
+  --foreground: #f3f4f6;
+  --card: #111827;
+  --sidebar: #0d121f;
+  --border: rgba(255, 255, 255, 0.06);
+  --brand: #e58a3c;
+  --muted: #9ca3af;
+}
+
+html {
+  color-scheme: dark;
 }
 
 body {
   background-color: var(--background);
   color: var(--foreground);
-  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
+  font-family: var(--font-sans), ui-sans-serif, system-ui, sans-serif;
+  background-image:
+    radial-gradient(ellipse 80% 50% at 10% -10%, rgba(229, 138, 60, 0.12), transparent 55%),
+    radial-gradient(ellipse 60% 40% at 100% 0%, rgba(56, 189, 248, 0.06), transparent 50%);
+  background-attachment: fixed;
+  min-height: 100vh;
+}
+
+/* Scrollbars sobrios */
+* {
+  scrollbar-width: thin;
+  scrollbar-color: #1f2937 transparent;
+}
+
+::selection {
+  background: rgba(229, 138, 60, 0.35);
+  color: #fff;
+}
+
+@layer utilities {
+  .text-balance {
+    text-wrap: balance;
+  }
 }