fix(scheduler): daily slot off-plan + cross-midnight resume (#8)

- Cross-midnight: unfinished yesterday seals ASAP with yesterday's stat_date;
  force seal ignores today's snapshot_at gate when stat_date < today.
- Off-plan already_completed: compare completion started_at (not finished_at)
  to today's planned slot; earlier → still run at slot for all daily tasks.
- Cold start: bootstrap task:state from task:last / seed markers.
- ensure_pending: do not glue new due onto a different day's unfinished state.
- run_if_needed(force): keep_scraped True for seal, False for CLI --force.
- Scheduler due_reader: pick up disk due_at each loop (seed→evening seal).

reaction_board/services/snapshot.py

@@ -142,12 +142,20 @@ class SnapshotService:
         return f"fans:seeded:{stat_date}"
 
     def run_if_needed(
-        self, *, date: str | None = None, force: bool = False
+        self,
+        *,
+        date: str | None = None,
+        force: bool = False,
+        keep_scraped: bool | None = None,
     ) -> SnapshotSummary:
         """视频快照（含 UP 头像补齐）；粉丝采集请用 ``run_fans_if_needed``。
 
         当日若仅有午夜 seed 壳且未 ``force``，直接返回等待晚间落盘，
         避免把「全员 skip」误标成 completed。
+
+        ``force`` + ``keep_scraped``：
+        - 晚间 seal / 断点续跑：``keep_scraped=True``（默认）保留已采 ok=1；
+        - CLI ``--force``：显式 ``keep_scraped=False`` 全量重采。
         """
         now = self._now()
         stat_date = date or shanghai_date(now)
@@ -155,9 +163,9 @@ class SnapshotService:
             raise ValueError(f"日期格式必须是 YYYY-MM-DD: {stat_date!r}")
         seeded = self.repo.kv_get(self.seeded_key(stat_date)) == "1"
         if force:
-            # 晚间 seal / 续跑：打穿 seed，保留已真实采集的 ok=1 作为进度。
+            ks = True if keep_scraped is None else bool(keep_scraped)
             return self.run_videos(
-                date=stat_date, force=True, keep_scraped=True,
+                date=stat_date, force=True, keep_scraped=ks,
             )
 
         completed = self.repo.kv_get(self.completed_key(stat_date)) == "1"