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.Test/Entity/TransactionCategoryTest.cs

@@ -0,0 +1,181 @@
+namespace WebApi.Test.Entity;
+
+/// <summary>
+/// TransactionCategory 实体测试
+/// </summary>
+public class TransactionCategoryTest : BaseTest
+{
+    [Fact]
+    public void Icon字段_应该接受Iconify标识符格式()
+    {
+        // Arrange
+        var category = new TransactionCategory
+        {
+            Name = "餐饮",
+            Type = TransactionType.Expense
+        };
+
+        // Act
+        category.Icon = "mdi:food";
+
+        // Assert
+        category.Icon.Should().Be("mdi:food");
+        category.Icon.Should().Contain(":");
+        category.Icon.Length.Should().BeLessThanOrEqualTo(50);
+    }
+
+    [Fact]
+    public void Icon字段_应该允许为空()
+    {
+        // Arrange & Act
+        var category = new TransactionCategory
+        {
+            Name = "交通",
+            Type = TransactionType.Expense,
+            Icon = null
+        };
+
+        // Assert
+        category.Icon.Should().BeNull();
+    }
+
+    [Fact]
+    public void Icon字段_应该遵守长度限制50字符()
+    {
+        // Arrange
+        var category = new TransactionCategory
+        {
+            Name = "购物",
+            Type = TransactionType.Expense
+        };
+
+        var validIcon = "mdi:shopping-cart"; // 合法长度
+        var tooLongIcon = new string('a', 51); // 超过50字符
+
+        // Act
+        category.Icon = validIcon;
+
+        // Assert
+        category.Icon.Should().Be(validIcon);
+        category.Icon.Length.Should().BeLessThanOrEqualTo(50);
+
+        // 验证长度限制（实际数据库插入时会被截断或报错）
+        tooLongIcon.Length.Should().BeGreaterThan(50);
+    }
+
+    [Fact]
+    public void IconKeywords字段_应该接受JSON数组格式()
+    {
+        // Arrange
+        var category = new TransactionCategory
+        {
+            Name = "餐饮",
+            Type = TransactionType.Expense
+        };
+
+        // Act
+        category.IconKeywords = "[\"food\", \"restaurant\", \"dining\"]";
+
+        // Assert
+        category.IconKeywords.Should().NotBeNullOrEmpty();
+        category.IconKeywords.Should().StartWith("[");
+        category.IconKeywords.Should().EndWith("]");
+        category.IconKeywords.Should().Contain("food");
+    }
+
+    [Fact]
+    public void IconKeywords字段_应该允许为空()
+    {
+        // Arrange & Act
+        var category = new TransactionCategory
+        {
+            Name = "交通",
+            Type = TransactionType.Expense,
+            IconKeywords = null
+        };
+
+        // Assert
+        category.IconKeywords.Should().BeNull();
+    }
+
+    [Fact]
+    public void IconKeywords字段_应该遵守长度限制200字符()
+    {
+        // Arrange
+        var category = new TransactionCategory
+        {
+            Name = "旅游",
+            Type = TransactionType.Expense
+        };
+
+        var validKeywords = "[\"travel\", \"vacation\", \"tourism\", \"trip\"]"; // 合法长度
+        var tooLongKeywords = "[" + string.Join(",", Enumerable.Repeat("\"keyword\"", 30)) + "]"; // 超过200字符
+
+        // Act
+        category.IconKeywords = validKeywords;
+
+        // Assert
+        category.IconKeywords.Should().Be(validKeywords);
+        category.IconKeywords.Length.Should().BeLessThanOrEqualTo(200);
+
+        // 验证长度限制
+        tooLongKeywords.Length.Should().BeGreaterThan(200);
+    }
+
+    [Fact]
+    public void TransactionCategory_应该继承自BaseEntity()
+    {
+        // Arrange & Act
+        var category = new TransactionCategory
+        {
+            Name = "测试分类",
+            Type = TransactionType.Expense
+        };
+
+        // Assert
+        category.Should().BeAssignableTo<BaseEntity>();
+        category.Id.Should().BeGreaterThan(0); // Snowflake ID
+        category.CreateTime.Should().BeCloseTo(DateTime.Now, TimeSpan.FromSeconds(1));
+    }
+
+    [Fact]
+    public void TransactionCategory_应该包含必需字段()
+    {
+        // Arrange & Act
+        var category = new TransactionCategory
+        {
+            Name = "餐饮",
+            Type = TransactionType.Expense,
+            Icon = "mdi:food",
+            IconKeywords = "[\"food\"]"
+        };
+
+        // Assert
+        category.Name.Should().NotBeNullOrEmpty();
+        category.Type.Should().Be(TransactionType.Expense);
+        category.Icon.Should().NotBeNullOrEmpty();
+        category.IconKeywords.Should().NotBeNullOrEmpty();
+    }
+
+    [Theory]
+    [InlineData("mdi:home")]
+    [InlineData("fa:shopping-cart")]
+    [InlineData("tabler:airplane")]
+    [InlineData("fluent:food-24-regular")]
+    public void Icon字段_应该支持多种图标集格式(string iconIdentifier)
+    {
+        // Arrange
+        var category = new TransactionCategory
+        {
+            Name = "测试",
+            Type = TransactionType.Expense
+        };
+
+        // Act
+        category.Icon = iconIdentifier;
+
+        // Assert
+        category.Icon.Should().Be(iconIdentifier);
+        category.Icon.Should().Contain(":");
+    }
+}