feat(api): 添加 BMI 分析端点 /api/bmi/analysis

- 新增 /api/bmi/analysis API 端点，提供 BMI 分析数据
- 返回当前体重、BMI、BMI状态、目标体重、预估达成天数等
- 基于近30天饮食和运动数据计算每日净消耗
- 更新测试框架支持 MySQL 和认证
- 修复其他 API 端点的用户隔离问题

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/test_web.py

@@ -7,13 +7,36 @@ from fastapi.testclient import TestClient
 
 from src.vitals.core import database as db
 from src.vitals.core.models import Exercise, Meal, Sleep, Weight, UserConfig
+from src.vitals.core.auth import create_token
 
 
 @pytest.fixture
 def client():
-    """创建测试客户端"""
+    """创建测试客户端（带认证）"""
     from src.vitals.web.app import app
-    return TestClient(app)
+
+    # 确保有测试用户
+    active_user = db.get_active_user()
+    if not active_user:
+        # 获取或创建默认用户
+        users = db.get_users()
+        if users:
+            active_user = users[0]
+            db.set_active_user(active_user.id)
+        else:
+            # 创建默认测试用户
+            from src.vitals.core.auth import hash_password
+            user_id = db.create_user("test_user", hash_password("test123"))
+            db.set_active_user(user_id)
+            active_user = db.get_user_by_id(user_id)
+
+    # 创建认证 token
+    token = create_token(active_user.id, active_user.name, active_user.is_admin)
+
+    # 创建带认证 cookie 的客户端
+    test_client = TestClient(app)
+    test_client.cookies.set("auth_token", token)
+    return test_client
 
 
 @pytest.fixture
@@ -282,3 +305,15 @@ class TestErrorHandling:
         """测试无效参数"""
         response = client.get("/api/exercises?days=abc")
         assert response.status_code == 422
+
+
+def test_bmi_analysis_endpoint(client):
+    """测试 BMI 分析 API"""
+    response = client.get("/api/bmi/analysis")
+    assert response.status_code == 200
+    data = response.json()
+    assert "current_weight" in data
+    assert "current_bmi" in data
+    assert "bmi_status" in data
+    assert "target_weight" in data
+    assert "estimated_days" in data