feat(backend): AI 服务层 — 千问流式 LLM + 月报解析 + 健康度计算 + 风险检测 + Copilot

- LLM 客户端：全部 SSE 流式输出，兼容 OpenAI 接口
- AI 月报解析：SSE 流式端点 POST /reports/{id}/parse
- 健康度计算引擎：四维评分（财务/经营/AI商业化/AI成本）
- 风险自动检测引擎：6 条规则自动检测指标越界
- AI Copilot：SSE 流式对话 POST /copilot/chat
- 权限中间件：角色级 + 字段级权限控制
- 测试：21 个新测试（健康度 8 + 风险检测 8 + 权限 5），总计 64 passed

backend/tests/test_health_calculator.py

@@ -0,0 +1,65 @@
+"""健康度计算引擎测试。"""
+
+from app.services.health_calculator import calculate_health_score, determine_trend
+
+
+class TestCalculateHealthScore:
+    """健康度评分计算。"""
+
+    def test_empty_data(self):
+        """空数据应返回全 0。"""
+        result = calculate_health_score({})
+        assert result["total_score"] == 0.0
+        assert result["financial_score"] == 0.0
+
+    def test_healthy_company(self):
+        """健康企业：跑道充足 + 营收增长 + 烧钱下降。"""
+        data = {
+            "revenue": {"yoy_change": "30"},
+            "cash_balance": {"runway_months": 18},
+            "burn_rate": {"trend": "down"},
+            "headcount": {"new_hires": 5, "departures": 1},
+            "key_metrics": [{"name": "ARR", "change": "+25%"}],
+        }
+        result = calculate_health_score(data)
+        assert result["total_score"] > 70
+        assert result["financial_score"] > 80
+
+    def test_unhealthy_company(self):
+        """不健康企业：跑道短 + 营收下滑 + 烧钱上升。"""
+        data = {
+            "revenue": {"yoy_change": "-20"},
+            "cash_balance": {"runway_months": 2},
+            "burn_rate": {"trend": "up"},
+            "headcount": {"new_hires": 0, "departures": 8},
+        }
+        result = calculate_health_score(data)
+        assert result["total_score"] < 50
+        assert result["financial_score"] < 30
+
+    def test_score_range(self):
+        """评分应在 0-100 范围内。"""
+        data = {
+            "revenue": {"yoy_change": "1000"},
+            "cash_balance": {"runway_months": 100},
+            "burn_rate": {"trend": "down"},
+        }
+        result = calculate_health_score(data)
+        for key, val in result.items():
+            assert 0 <= val <= 100
+
+
+class TestDetermineTrend:
+    """趋势判断。"""
+
+    def test_up(self):
+        assert determine_trend(80, 60) == "up"
+
+    def test_down(self):
+        assert determine_trend(50, 70) == "down"
+
+    def test_stable(self):
+        assert determine_trend(60, 62) == "stable"
+
+    def test_no_previous(self):
+        assert determine_trend(70, None) == "stable"