feat(aigc): add travel postcard AIGC feature

Add complete travel postcard AIGC creation workflow including:
- New AIGC pages: template selection home, result detail, and history records
- Reusable UI components: template card, flow steps, result preview, action buttons, record lists
- Static assets including template images, fonts and styles
- Updated TopNavBar component to support menu button alignment
- Register new AIGC page routes in pages.json
- Add mock data for templates, user records and result details

src/pages-aigc/detail/components/ResultPreview/index.vue

@@ -0,0 +1,25 @@
+<template>
+  <view class="result-preview" :style="{ '--result-accent': result.accent }">
+    <image class="result-preview-image" :src="result.cover" mode="aspectFill" />
+    <view class="result-preview-shade" />
+
+    <view class="result-preview-caption">
+      <text class="result-preview-badge">{{ result.variantLabel }}</text>
+      <text class="result-preview-title">{{ result.title }}</text>
+      <text class="result-preview-desc">{{ result.desc }}</text>
+    </view>
+  </view>
+</template>
+
+<script setup>
+defineProps({
+  result: {
+    type: Object,
+    default: () => ({}),
+  },
+});
+</script>
+
+<style scoped lang="scss">
+@import "./styles/index.scss";
+</style>