refactor: 4层架构重构 + 饮食VLM接入 + 多项修复

- 后端: remaining_endpoints拆分为6个独立文件
- 后端: AI Agent Handler从ai_chat_endpoints抽取为7个独立处理器
- 后端: 食物识别prompt改为输出结构化JSON
- 前端: 饮食识别从Mock替换为真实VLM API调用
- 前端: 首页图片上传URL修复(/api/upload→/api/files/upload)
- 前端: 拍饮食按钮导航到独立DietCapturePage
- 前端: 删除无用agent_bar.dart
- 前端: 修复widget_test.dart过期属性名
- 前端: 恢复ServicePackageCard和详情页
- 新增6份实施文档(情况/问诊/报告/建档/日历/视觉统一)

backend/src/Health.WebApi/Endpoints/diet_endpoints.cs

@@ -0,0 +1,49 @@
+namespace Health.WebApi.Endpoints;
+
+public static class DietEndpoints
+{
+    public static void MapDietEndpoints(this WebApplication app)
+    {
+        var group = app.MapGroup("/api/diet-records").RequireAuthorization();
+
+        group.MapGet("/", async (string? date, string? mealType, HttpContext http, AppDbContext db, CancellationToken ct) =>
+        {
+            var userId = GetUserId(http);
+            var query = db.DietRecords.Include(d => d.FoodItems).Where(d => d.UserId == userId);
+            if (DateOnly.TryParse(date, out var d)) query = query.Where(r => r.RecordedAt == d);
+            if (Enum.TryParse<MealType>(mealType, ignoreCase: true, out var mt)) query = query.Where(r => r.MealType == mt);
+            var records = await query.OrderByDescending(r => r.RecordedAt).ToListAsync(ct);
+            return Results.Ok(new { code = 0, data = records, message = (string?)null });
+        });
+
+        group.MapPost("/", async (CreateDietRequest req, HttpContext http, AppDbContext db, CancellationToken ct) =>
+        {
+            var userId = GetUserId(http);
+            var record = new DietRecord
+            {
+                Id = Guid.NewGuid(), UserId = userId, MealType = req.MealType,
+                TotalCalories = req.TotalCalories, HealthScore = req.HealthScore, RecordedAt = req.RecordedAt ?? DateOnly.FromDateTime(DateTime.Now),
+            };
+            if (req.FoodItems != null)
+                foreach (var fi in req.FoodItems)
+                    record.FoodItems.Add(new DietFoodItem { Id = Guid.NewGuid(), Name = fi.Name, Portion = fi.Portion, Calories = fi.Calories, ProteinGrams = fi.ProteinGrams, CarbsGrams = fi.CarbsGrams, FatGrams = fi.FatGrams, Warning = fi.Warning, SortOrder = fi.SortOrder });
+            db.DietRecords.Add(record);
+            await db.SaveChangesAsync(ct);
+            return Results.Ok(new { code = 0, data = new { record.Id }, message = (string?)null });
+        });
+
+        group.MapDelete("/{id:guid}", async (Guid id, HttpContext http, AppDbContext db, CancellationToken ct) =>
+        {
+            var userId = GetUserId(http);
+            var record = await db.DietRecords.FirstOrDefaultAsync(r => r.Id == id && r.UserId == userId, ct);
+            if (record != null) { db.DietRecords.Remove(record); await db.SaveChangesAsync(ct); }
+            return Results.Ok(new { code = 0, data = new { success = true }, message = (string?)null });
+        });
+    }
+
+    private static Guid GetUserId(HttpContext http) =>
+        Guid.TryParse(http.User.FindFirst(System.Security.Claims.ClaimTypes.NameIdentifier)?.Value, out var id) ? id : Guid.Empty;
+}
+
+public sealed record CreateDietRequest(MealType MealType, int? TotalCalories, int? HealthScore, DateOnly? RecordedAt, List<FoodItemDto>? FoodItems);
+public sealed record FoodItemDto(string Name, string? Portion, int? Calories, decimal? ProteinGrams, decimal? CarbsGrams, decimal? FatGrams, string? Warning, int SortOrder);