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/IconCandidate.cs

@@ -0,0 +1,22 @@
+namespace Service.IconSearch;
+
+/// <summary>
+/// 图标候选对象
+/// </summary>
+public record IconCandidate
+{
+    /// <summary>
+    /// 图标集名称
+    /// </summary>
+    public string CollectionName { get; init; } = string.Empty;
+
+    /// <summary>
+    /// 图标名称
+    /// </summary>
+    public string IconName { get; init; } = string.Empty;
+
+    /// <summary>
+    /// 图标标识符（格式：{collectionName}:{iconName}）
+    /// </summary>
+    public string IconIdentifier => $"{CollectionName}:{IconName}";
+}