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

.temp_verify_fix.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Text.Json;
+using System.Linq;
+using System.Collections.Generic;
+
+// 模拟修复后的响应类型
+public record IconifyApiResponse
+{
+    [System.Text.Json.Serialization.JsonPropertyName("icons")]
+    public List<string>? Icons { get; init; }
+}
+
+public class IconCandidate
+{
+    public string CollectionName { get; set; } = string.Empty;
+    public string IconName { get; set; } = string.Empty;
+    public string IconIdentifier => $"{CollectionName}:{IconName}";
+}
+
+class Program
+{
+    static void Main()
+    {
+        // 从 Iconify API 获取的实际响应
+        var jsonResponse = @"{""icons"":[""svg-spinners:wind-toy"",""material-symbols:smart-toy"",""mdi:toy-brick"",""tabler:horse-toy"",""game-icons:toy-mallet""]}";
+        
+        Console.WriteLine("=== 图标搜索功能验证 ===\n");
+        Console.WriteLine($"1. Iconify API 响应格式: {jsonResponse.Substring(0, 100)}...\n");
+        
+        // 反序列化
+        var apiResponse = JsonSerializer.Deserialize<IconifyApiResponse>(jsonResponse);
+        Console.WriteLine($"2. 反序列化成功，图标数量: {apiResponse?.Icons?.Count ?? 0}\n");
+        
+        // 解析为 IconCandidate
+        var candidates = apiResponse?.Icons?
+            .Select(iconStr =>
+            {
+                var parts = iconStr.Split(':', 2);
+                if (parts.Length != 2) return null;
+                
+                return new IconCandidate
+                {
+                    CollectionName = parts[0],
+                    IconName = parts[1]
+                };
+            })
+            .Where(c => c != null)
+            .Cast<IconCandidate>()
+            .ToList() ?? new List<IconCandidate>();
+        
+        Console.WriteLine($"3. 解析为 IconCandidate 列表，数量: {candidates.Count}\n");
+        Console.WriteLine("4. 图标列表:");
+        foreach (var icon in candidates)
+        {
+            Console.WriteLine($"   - {icon.IconIdentifier} (Collection: {icon.CollectionName}, Name: {icon.IconName})");
+        }
+        
+        Console.WriteLine("\n✅ 验证成功！图标搜索功能已修复。");
+    }
+}