style(theme): expand color palettes and refine dark mode styles

- Expand CSS variables for primary and secondary colors to include full 50-950 scales in `main.css`.
- Update components to reference specific color shades (e.g., `primary-400`, `secondary-200`) instead of generic variables.
- Add dark mode background and text colors to Events, Hall of Fame, and Index sections.
- Adjust image aspect ratio in the Events component.

app/error.vue

@@ -164,7 +164,7 @@ const errorColor = computed(() => {
               <button
                 @click="goHome"
                 class="px-5 py-2.5 rounded-md text-white font-medium transition-colors flex items-center gap-2"
-                style="background-color: var(--color-primary)"
+                style="background-color: var(--color-primary-400)"
               >
                 <span>返回首页</span>
               </button>