feat(ai): v2 新增 GenerateReport RPC + ReportService

第 9 个 RPC GenerateReport（学情报告生成）：data-ana 学情数据 → LLM 生成 → 结构化提取

新增 ReportService 业务编排层 + GenerateReportRequest/GeneratedReport 模型

gRPC servicer + HTTP POST /v1/ai/generate/report（权限 ai:report:generate）

proto_gen 重新生成 + 测试覆盖（servicer/service/HTTP/模型/权限 共 26 用例）

402 测试通过，覆盖率 88.5%

services/ai/tests/test_main_app.py

@@ -328,6 +328,75 @@ async def test_optimize_expression(client: httpx.AsyncClient) -> None:
     assert body["data"]["degraded"] is True
 
 
+# ---------------------------------------------------------------------------
+# Generate report endpoint
+# ---------------------------------------------------------------------------
+
+
+async def test_generate_report_class_summary(client: httpx.AsyncClient) -> None:
+    """POST /v1/ai/generate/report with class_summary returns degraded report (no LLM key)."""
+    resp = await client.post(
+        "/v1/ai/generate/report",
+        json={"class_id": "c-1", "report_type": "class_summary"},
+    )
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["success"] is True
+    # 测试环境无 LLM API key → degraded
+    assert body["data"]["degraded"] is True
+    assert "id" in body["data"]
+
+
+async def test_generate_report_student_detail(client: httpx.AsyncClient) -> None:
+    """POST /v1/ai/generate/report with student_detail + student_id."""
+    resp = await client.post(
+        "/v1/ai/generate/report",
+        json={
+            "class_id": "c-1",
+            "report_type": "student_detail",
+            "student_id": "s-001",
+        },
+    )
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["success"] is True
+    assert body["data"]["degraded"] is True
+
+
+async def test_generate_report_invalid_type(client: httpx.AsyncClient) -> None:
+    """POST /v1/ai/generate/report with invalid report_type returns 422."""
+    resp = await client.post(
+        "/v1/ai/generate/report",
+        json={"class_id": "c-1", "report_type": "invalid_type"},
+    )
+    assert resp.status_code == 422
+
+
+async def test_generate_report_missing_class_id(client: httpx.AsyncClient) -> None:
+    """POST /v1/ai/generate/report without class_id returns 422."""
+    resp = await client.post(
+        "/v1/ai/generate/report",
+        json={"report_type": "class_summary"},
+    )
+    assert resp.status_code == 422
+
+
+async def test_generate_report_permission_denied(prod_client: httpx.AsyncClient) -> None:
+    """Student role attempting to generate report returns 403."""
+    resp = await prod_client.post(
+        "/v1/ai/generate/report",
+        json={"class_id": "c-1", "report_type": "class_summary"},
+        headers={
+            "X-User-Id": "student-1",
+            "X-User-Role": "student",
+        },
+    )
+    assert resp.status_code == 403
+    body = resp.json()
+    assert body["success"] is False
+    assert body["error"]["code"] == "AI_FORBIDDEN"
+
+
 # ---------------------------------------------------------------------------
 # Lesson plan endpoints
 # ---------------------------------------------------------------------------