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

Service/IconSearch/ISearchKeywordGeneratorService.cs

@@ -0,0 +1,14 @@
+namespace Service.IconSearch;
+
+/// <summary>
+/// 搜索关键字生成服务接口
+/// </summary>
+public interface ISearchKeywordGeneratorService
+{
+    /// <summary>
+    /// 根据分类名称生成搜索关键字
+    /// </summary>
+    /// <param name="categoryName">分类名称</param>
+    /// <returns>搜索关键字数组</returns>
+    Task<List<string>> GenerateKeywordsAsync(string categoryName);
+}