feat(growth): same-day 1-day baselines for new videos

Let 1-day view growth use a zero baseline for videos published today, and the first successful sample for older videos ingested today, without mixing those into 7/30-day rankings.

tests/web_fixtures.py

@@ -138,7 +138,7 @@ def build_db(tmp: str | Path) -> Path:
                 day, 37754047, follower=1000 + index * 10, following=5,
                 ok=True, captured_at=ts(day) + 60,
             )
-        # 103 只有最后一天快照，用于验证样本不足；104 另加一条失败快照
+        # 103 只有最后一天快照（发布日=快照日，近 1 日相对 0）；104 另加一条失败快照
         repo.upsert_snapshot(
             DATES[-1], 103,
             metrics={"view": 120, "like": 5, "coin": 1, "favorite": 2, "share": 0, "reply": 1, "danmaku": 1},