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

WebApi/appsettings.json

@@ -102,5 +102,14 @@
         "ColorCode": "#E0E0E0"
       }
     }
+  },
+  "IconifySettings": {
+    "ApiUrl": "https://api.iconify.design/search",
+    "DefaultLimit": 20,
+    "MaxRetryCount": 3,
+    "RetryDelayMs": 1000
+  },
+  "SearchKeywordSettings": {
+    "KeywordPromptTemplate": "为以下中文分类名称生成3-5个相关的英文搜索关键字，用于搜索图标：{categoryName}。输出格式为JSON数组，例如：[\"food\", \"restaurant\", \"dining\"]。"
   }
 }