feat: add gift points toast and refactor useTemplate layout

Add a new gift points notification toast to the AIGC home page for new user signup rewards.
Restructure the useTemplate page's layout and SCSS, split the content container and add dedicated popup host for modal steps.
Remove the unused UploadTemplatePreview component and all related references from the codebase.

src/pages-aigc/home/components/GiftPointsToast/index.vue

@@ -0,0 +1,37 @@
+<template>
+  <view v-if="visible" class="gift-points-toast" role="status">
+    <text class="gift-points-badge">{{ title }}</text>
+    <text class="gift-points-message">{{ message }}</text>
+    <view class="gift-points-close" @tap="handleClose">
+      <uni-icons type="closeempty" size="20" color="#ffffff" />
+    </view>
+  </view>
+</template>
+
+<script setup>
+defineProps({
+  visible: {
+    type: Boolean,
+    default: true,
+  },
+  title: {
+    type: String,
+    default: "300积分已到账",
+  },
+  message: {
+    type: String,
+    default: "新用户权益已发放，可用于图片版或动效视频版内容升级。",
+  },
+});
+
+const emit = defineEmits(["close", "update:visible"]);
+
+const handleClose = () => {
+  emit("update:visible", false);
+  emit("close");
+};
+</script>
+
+<style scoped lang="scss">
+@import "./styles/index.scss";
+</style>