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

Entity/TransactionCategory.cs

@@ -1,4 +1,4 @@
-namespace Entity;
+namespace Entity;
 
 /// <summary>
 /// 交易分类
@@ -16,9 +16,14 @@ public class TransactionCategory : BaseEntity
     public TransactionType Type { get; set; }
 
     /// <summary>
-    /// 图标（SVG格式，JSON数组存储5个图标供选择）
-    /// 示例：["<svg>...</svg>", "<svg>...</svg>", ...]
+    /// 图标（Iconify标识符格式：{collection}:{name}，如"mdi:home"）
     /// </summary>
-    [Column(StringLength = -1)]
+    [Column(StringLength = 50)]
     public string? Icon { get; set; }
+
+    /// <summary>
+    /// 搜索关键字（JSON数组，如["food", "restaurant", "dining"]）
+    /// </summary>
+    [Column(StringLength = 200)]
+    public string? IconKeywords { get; set; }
 }