feat: Add clickable dashboard cards and theme color selector

- Dashboard cards now link to list page when clicked (except + button)
- Added theme color selector in Settings (orange, teal, red, green, blue)
- Theme persists in localStorage

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

client/public/locales/en/common.json

@@ -348,6 +348,14 @@
             "round_prices": {
                 "label": "Round prices",
                 "tooltip": "Round prices to the nearest whole number."
+            },
+            "theme_color": {
+                "label": "Theme Color",
+                "orange": "Orange",
+                "teal": "Teal",
+                "red": "Red",
+                "green": "Green",
+                "blue": "Blue"
             }
         },
         "backup": {