feat(web): add fan date range modes and delta column

tests/test_web_server.py

@@ -110,6 +110,26 @@ def test_readonly_routes_and_static():
                 point["stat_date"] >= "2026-10-18"
                 for point in fans["recent_points"]
             )
+            assert all("delta" in point for point in fans["recent_points"])
+
+            status, _, payload = running.request(
+                "/api/fans?start=2026-10-29&end=2026-10-31"
+            )
+            assert status == 200
+            data = json.loads(payload)["data"]
+            assert data["mode"] == "daily"
+            assert data["dates"] == ["2026-10-29", "2026-10-30", "2026-10-31"]
+
+            running.db.write(lambda conn: conn.execute(
+                "INSERT OR REPLACE INTO up_stat"
+                "(stat_date, mid, follower, following, captured_at, ok) "
+                "VALUES ('2025-01-01', 37754047, 500, NULL, 1, 1)"
+            ))
+            status, _, payload = running.request(
+                "/api/fans?start=2025-01-01&end=2026-10-31"
+            )
+            assert status == 200
+            assert json.loads(payload)["data"]["mode"] == "monthly"
 
             status, headers, payload = running.request("/api/videos", method="HEAD")
             assert status == 200 and payload == b""