Add configurable news research backfill and coverage reporting

Allow selecting a historical start time and checking unfinished news before enabling analysis. Report enrolled work outside the selected range and use the active server boundary while retaining paused drafts. Cover date validation, queue carryover, task completion and cross-tab responses.

scripts/smoke_news_research.py

@@ -382,12 +382,25 @@ async def main():
             published_skill = await s.get(SkillVersion, node.published_version_id)
             published_skill.content = valid_content
             await s.commit()
+        previous_start = (await client.get("/api/risk/settings")).json()["data"]["start_at"]
+        selected_start = "2026-10-01T00:00:00+08:00"
+        with patch.object(model_service, "complete", side_effect=AssertionError("核查和无效时间不应调用模型")):
+            for invalid in ["2026-10-01T00:00:00", "2999-01-01T00:00:00Z"]:
+                assert (await client.post("/api/risk/enable", json={"start_at": invalid})).status_code == 422
+                assert (await client.get("/api/risk/coverage", params={"start_at": invalid})).status_code == 422
+            report = await client.get("/api/risk/coverage", params={"start_at": selected_start})
+            assert report.status_code == 200, report.text
+            assert report.json()["data"]["start_at"] == "2026-09-30T16:00:00Z"
+            assert set(report.json()["data"]["outside"]) == {"unprocessed", "stale", "pending", "processing", "failed"}
+        assert (await client.get("/api/risk/settings")).json()["data"]["start_at"] == previous_start
         with patch.object(model_service, "complete", validation):
-            response = await client.post("/api/risk/enable")
+            response = await client.post("/api/risk/enable", json={"start_at": selected_start})
             assert response.status_code == 200, response.text
+            assert response.json()["data"]["start_at"] == "2026-09-30T16:00:00Z"
         assert (await client.get("/api/risk/settings")).json()["data"][
             "enabled"
         ] is True
+        assert (await client.get("/api/risk/settings")).json()["data"]["start_at"] == "2026-09-30T16:00:00Z"
         assert (await client.post("/api/risk/enable")).status_code == 409
         assert (await client.post("/api/risk/pause")).status_code == 200
         for action in ("pause", "save"):
@@ -408,11 +421,12 @@ async def main():
                 return await validation(provider, skill, payload, schema)
 
             with patch.object(model_service, "complete", interrupted_validation):
-                response = await client.post("/api/risk/enable")
+                response = await client.post("/api/risk/enable", json={"start_at": "2026-09-01T00:00:00Z"})
                 assert response.status_code == 409, response.text
             assert (await client.get("/api/risk/settings")).json()["data"][
                 "enabled"
             ] is False
+            assert (await client.get("/api/risk/settings")).json()["data"]["start_at"] == "2026-09-30T16:00:00Z"
         package_id = (await client.get(f"/api/risk/news/{news_id}/packages")).json()[
             "data"
         ][0]["id"]