Add dark mode with system preference auto-detection

All user-facing components now support dark mode via prefers-color-scheme.
- Dark backgrounds: gray-950/900/800
- Dark text: gray-100/200/300/400
- Orange brand colors adapt with darker tints
- Glass effects work in both modes
- Skeletons, cards, filters, bottom sheet all themed
- Google Maps InfoWindow stays light (maps don't support dark)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/app/globals.css

@@ -3,7 +3,7 @@
 :root {
   --background: #ffffff;
   --foreground: #171717;
-  color-scheme: light only;
+  color-scheme: light dark;
 }
 
 @theme inline {
@@ -14,16 +14,11 @@
 
 @media (prefers-color-scheme: dark) {
   :root {
-    --background: #ffffff;
-    --foreground: #171717;
-    color-scheme: light only;
+    --background: #0a0a0a;
+    --foreground: #ededed;
   }
 }
 
-* {
-  color-scheme: light only;
-}
-
 body {
   background: var(--background);
   color: var(--foreground);
@@ -34,11 +29,7 @@ html, body, #__next {
   margin: 0;
 }
 
-input, select, textarea {
-  color-scheme: light;
-}
-
-/* Force Google Maps InfoWindow to light mode */
+/* Force Google Maps InfoWindow to light mode (maps don't support dark) */
 .gm-style .gm-style-iw,
 .gm-style .gm-style-iw-c,
 .gm-style .gm-style-iw-d,