feat: match original theme to authentic 1987 DLR livery

Set the original colour scheme's typeface and palette to the 1987
Docklands Light Railway P86/P89 stock.

- Use the Rockwell slab serif (the original DLR branding typeface) for the
  original theme, with Rokkitt loaded as a free fallback for systems
  without Rockwell installed.
- Flip the palette to be blue-dominant: blue body/skirt as the field, red
  band/doors as the accent, white stripes, matching the rolling stock.

styles.css

@@ -19,16 +19,20 @@
   --button-active-text: #ffffff;
 }
 
-/* Original DLR — 1987 red, white and blue */
+/* Original DLR — 1987 P86/P89 livery: blue body and skirt, red band and
+   doors, white stripes. Blue is the dominant field, red the accent.
+   1987 branding used the Rockwell slab serif; Rokkitt is a free fallback for
+   systems without Rockwell installed. */
 [data-theme="original"] {
-  --bg: #c8102e;
-  --surface: #002b5c;
-  --text: #f5f0e1;
-  --message: #f5f0e1;
-  --button-bg: #002b5c;
-  --button-text: #f5f0e1;
-  --button-active-bg: #f5f0e1;
-  --button-active-text: #002b5c;
+  --font-stack: Rockwell, "Rockwell Nova", Rokkitt, Georgia, serif;
+  --bg: #1f3a93;
+  --surface: #c8102e;
+  --text: #ffffff;
+  --message: #ffffff;
+  --button-bg: #c8102e;
+  --button-text: #ffffff;
+  --button-active-bg: #ffffff;
+  --button-active-text: #1f3a93;
 }
 
 * {