fix: default seed_at to 00:00 (HH:MM)

Keep daily tasks next_run=0 startup catch-up; only move midnight
seed schedule default from 00:01 to 00:00 across config/docs/tests.

reaction_board/config.py

@@ -84,7 +84,7 @@ DEFAULT_CONFIG: dict[str, Any] = {
     "schedule": {
         "discover_minutes": 60,
         "snapshot_at": "23:15",
-        "seed_at": "00:01",
+        "seed_at": "00:00",
         "candidate_ttl_days": 7,
         "recent_snapshot_minutes": 60,
         "recent_video_days": 2,
@@ -454,7 +454,7 @@ def _build_config(data: Mapping[str, Any], path: Path) -> AppConfig:
     snapshot_at = _as_str(sched_raw.get("snapshot_at", "23:15"), "schedule.snapshot_at")
     if not _SNAPSHOT_AT_RE.match(snapshot_at):
         raise ConfigError("schedule.snapshot_at 必须是 HH:MM（24 小时制）")
-    seed_at = _as_str(sched_raw.get("seed_at", "00:01"), "schedule.seed_at")
+    seed_at = _as_str(sched_raw.get("seed_at", "00:00"), "schedule.seed_at")
     if not _SNAPSHOT_AT_RE.match(seed_at):
         raise ConfigError("schedule.seed_at 必须是 HH:MM（24 小时制）")
     schedule = ScheduleConfig(