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/IconSearchService.cs

@@ -0,0 +1,48 @@
+namespace Service.IconSearch;
+
+public class IconSearchService(
+    ISearchKeywordGeneratorService keywordGeneratorService,
+    IIconifyApiService iconifyApiService,
+    ITransactionCategoryRepository categoryRepository,
+    ILogger<IconSearchService> logger
+) : IIconSearchService
+{
+    public async Task<List<string>> GenerateSearchKeywordsAsync(string categoryName)
+    {
+        var keywords = await keywordGeneratorService.GenerateKeywordsAsync(categoryName);
+        return keywords;
+    }
+
+    public async Task<List<IconCandidate>> SearchIconsAsync(List<string> keywords, int limit = 20)
+    {
+        if (keywords == null || keywords.Count == 0)
+        {
+            logger.LogWarning("搜索关键字为空");
+            return [];
+        }
+
+        var icons = await iconifyApiService.SearchIconsAsync(keywords, limit);
+        logger.LogInformation("搜索到 {Count} 个图标候选", icons.Count);
+        return icons;
+    }
+
+    public async Task UpdateCategoryIconAsync(long categoryId, string iconIdentifier)
+    {
+        if (string.IsNullOrWhiteSpace(iconIdentifier))
+        {
+            throw new ArgumentException("图标标识符不能为空", nameof(iconIdentifier));
+        }
+
+        var category = await categoryRepository.GetByIdAsync(categoryId);
+        if (category == null)
+        {
+            throw new Exception($"分类不存在，ID：{categoryId}");
+        }
+
+        category.Icon = iconIdentifier;
+        category.IconKeywords = null;
+        await categoryRepository.UpdateAsync(category);
+
+        logger.LogInformation("更新分类 {CategoryId} 的图标为 {IconIdentifier}", categoryId, iconIdentifier);
+    }
+}