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

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+"""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"

backend/tests/test_permissions.py

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+"""权限中间件测试。"""
+
+from types import SimpleNamespace
+
+from app.core.permissions import filter_fields, require_min_role, require_role, ROLE_HIERARCHY
+
+
+class TestRoleHierarchy:
+    """角色层级。"""
+
+    def test_admin_highest(self):
+        assert ROLE_HIERARCHY["admin"] > ROLE_HIERARCHY["investor"]
+        assert ROLE_HIERARCHY["admin"] > ROLE_HIERARCHY["founder"]
+
+    def test_investor_above_founder(self):
+        assert ROLE_HIERARCHY["investor"] > ROLE_HIERARCHY["founder"]
+
+
+class TestFilterFields:
+    """字段级权限过滤。"""
+
+    def test_investor_sees_all(self):
+        """investor 可见全部字段。"""
+        data = {"name": "公司A", "total_funding": "1亿", "description": "测试"}
+        user = SimpleNamespace(role="investor")
+        result = filter_fields("company", data, user)
+        assert result == data
+
+    def test_founder_filtered(self):
+        """founder 只能看限定字段。"""
+        data = {"name": "公司A", "total_funding": "1亿", "description": "测试", "id": "123"}
+        user = SimpleNamespace(role="founder")
+        result = filter_fields("company", data, user)
+        assert "name" in result
+        assert "id" in result
+        assert "total_funding" not in result
+
+    def test_admin_sees_all(self):
+        """admin 可见全部字段。"""
+        data = {"name": "公司A", "total_funding": "1亿"}
+        user = SimpleNamespace(role="admin")
+        result = filter_fields("company", data, user)
+        assert result == data

backend/tests/test_risk_engine.py

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+"""风险检测引擎测试。"""
+
+from app.services.risk_engine import detect_risks
+
+
+class TestDetectRisks:
+    """风险自动检测。"""
+
+    def test_empty_data(self):
+        """空数据不应检测到风险。"""
+        risks = detect_risks({}, "company-1")
+        assert len(risks) == 0
+
+    def test_low_runway_critical(self):
+        """跑道 < 3 月应触发 critical 风险。"""
+        data = {"cash_balance": {"runway_months": 2}}
+        risks = detect_risks(data, "company-1")
+        assert any(r["severity"] == "critical" for r in risks)
+        assert any("3 个月" in r["title"] for r in risks)
+
+    def test_low_runway_warning(self):
+        """跑道 3-6 月应触发 high 风险。"""
+        data = {"cash_balance": {"runway_months": 4}}
+        risks = detect_risks(data, "company-1")
+        assert any(r["severity"] == "high" and "6 个月" in r["title"] for r in risks)
+
+    def test_burn_rate_up(self):
+        """烧钱率上升应触发 medium 风险。"""
+        data = {"burn_rate": {"trend": "up"}}
+        risks = detect_risks(data, "company-1")
+        assert any(r["severity"] == "medium" and "烧钱率" in r["title"] for r in risks)
+
+    def test_revenue_decline(self):
+        """营收下滑应触发 high 风险。"""
+        data = {"revenue": {"yoy_change": "-15"}}
+        risks = detect_risks(data, "company-1")
+        assert any(r["severity"] == "high" and "营收" in r["title"] for r in risks)
+
+    def test_high_departures(self):
+        """高离职率应触发 medium 风险。"""
+        data = {"headcount": {"new_hires": 2, "departures": 8}}
+        risks = detect_risks(data, "company-1")
+        assert any(r["severity"] == "medium" and "流失" in r["title"] for r in risks)
+
+    def test_healthy_company_no_risks(self):
+        """健康企业不应检测到风险。"""
+        data = {
+            "revenue": {"yoy_change": "20"},
+            "cash_balance": {"runway_months": 18},
+            "burn_rate": {"trend": "down"},
+            "headcount": {"new_hires": 5, "departures": 1},
+        }
+        risks = detect_risks(data, "company-1")
+        assert len(risks) == 0
+
+    def test_company_id_in_risks(self):
+        """风险事件应包含 company_id。"""
+        data = {"cash_balance": {"runway_months": 2}}
+        risks = detect_risks(data, "test-company-id")
+        for r in risks:
+            assert r["company_id"] == "test-company-id"