refactor: replace theme color utility classes with direct hex values

remove unused theme color background utility classes from background.scss,
swap all instances of bg-theme-color-50 and bg-theme-color-500 with their
corresponding hex values across vue components, and update bg-liner gradient
to use direct hex colors instead of theme variables

src/pages/ChatModule/OpenMapComponent/index.vue

@@ -3,7 +3,7 @@
         <!-- 占位撑开 -->
         <view class="w-vw"></view>
         <view class="flex flex-items-center flex-justify-between p-12 border-box" @click="openMap">
-            <view class="rounded-16 p-16 bg-theme-color-50">
+            <view class="rounded-16 p-16 bg-[#F0F8F3]">
                 <view class="w-32 h-32 rounded-full bg-white flex flex-items-center flex-justify-center">
                     <uni-icons type="location" size="16" color="#171717" />
                 </view>