chore: migrate remaining ECharts components to Chart.js

- Migrated 4 components from ECharts to Chart.js:
  * MonthlyExpenseCard.vue (折线图)
  * DailyTrendChart.vue (双系列折线图)
  * ExpenseCategoryCard.vue (环形图)
  * BudgetChartAnalysis.vue (仪表盘 + 多种图表)

- Removed all ECharts imports and environment variable switches
- Unified all charts to use BaseChart.vue component
- Build verified: pnpm build success ✓
- No echarts imports remaining ✓

Refs: openspec/changes/migrate-remaining-echarts-to-chartjs

Web/src/components/Icon.vue

@@ -0,0 +1,54 @@
+<template>
+  <span
+    class="iconify"
+    :data-icon="iconIdentifier"
+    :style="iconStyle"
+  ></span>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+
+interface Props {
+  iconIdentifier: string
+  width?: string | number
+  height?: string | number
+  color?: string
+  size?: string | number
+}
+
+const props = withDefaults(defineProps<Props>(), {
+  width: '1em',
+  height: '1em',
+  color: undefined,
+  size: undefined
+})
+
+const iconStyle = computed(() => {
+  const style: Record<string, string> = {}
+  
+  if (props.width) {
+    style.width = typeof props.width === 'number' ? `${props.width}px` : props.width
+  }
+  if (props.height) {
+    style.height = typeof props.height === 'number' ? `${props.height}px` : props.height
+  }
+  if (props.color) {
+    style.color = props.color
+  }
+  if (props.size) {
+    const size = typeof props.size === 'number' ? `${props.size}px` : props.size
+    style.fontSize = size
+  }
+  
+  return style
+})
+</script>
+
+<style scoped lang="scss">
+.iconify {
+  display: inline-block;
+  vertical-align: middle;
+  line-height: 1;
+}
+</style>