feat(scheduler): add snapshot-seed CLI and 10m seed deferral

Add `python app.py snapshot-seed [--date]` (offline clone, Debian /
docker compose exec friendly). When seed fires while full-site snapshot
is running, or last_completed is missing (no_source), record skip as
non-success and retry in 10 minutes until a real seed succeeds; fans
and quiet-window rules unchanged.

tests/test_web_queries.py

@@ -711,6 +711,51 @@ def test_snapshot_failed_next_run_retries_soon_not_next_day():
             db.close()
 
 
+def test_snapshot_seed_skip_next_run_retries_ten_minutes():
+    import json
+    from datetime import datetime
+    from reaction_board.timeutil import SHANGHAI_TZ, next_daily_run
+
+    with tempfile.TemporaryDirectory() as tmp:
+        db, q = setup(tmp)
+        try:
+            repo = Repository(db)
+            finished = int(datetime(2026, 11, 1, 0, 0, 0, tzinfo=SHANGHAI_TZ).timestamp())
+            repo.kv_set(
+                "task:last:snapshot_seed",
+                json.dumps({
+                    "name": "snapshot_seed", "ok": False, "skipped": True,
+                    "started_at": finished - 1, "finished_at": finished,
+                    "error": "snapshot_running",
+                    "summary": {"skipped": True, "reason": "snapshot_running"},
+                }),
+            )
+            DASHBOARD_CACHE.clear()
+            system = q.system()
+            assert system["next_runs"]["snapshot_seed"] == finished + 600
+            assert system["next_runs"]["snapshot_seed"] != int(
+                next_daily_run(finished, "00:00")
+            )
+            # skip 不算 errors
+            assert not any(e["task"] == "snapshot_seed" for e in system["errors"])
+
+            # no_source 同样 10 分钟
+            repo.kv_set(
+                "task:last:snapshot_seed",
+                json.dumps({
+                    "name": "snapshot_seed", "ok": False, "skipped": True,
+                    "started_at": finished - 1, "finished_at": finished,
+                    "error": "no_source",
+                    "summary": {"skipped": True, "reason": "no_source"},
+                }),
+            )
+            DASHBOARD_CACHE.clear()
+            system = q.system()
+            assert system["next_runs"]["snapshot_seed"] == finished + 600
+        finally:
+            db.close()
+
+
 
 def test_overview_adjacent_previous_with_seed_and_dual_fields():
     """seed 当日行存在时，播放增量按片相邻成功日；overview 暴露更新时刻与总数。"""
@@ -964,6 +1009,7 @@ def main_test():
     test_snapshot_recent_next_run_follows_completion()
     test_snapshot_recent_next_run_defers_quiet_window_and_retry_on_skip()
     test_snapshot_failed_next_run_retries_soon_not_next_day()
+    test_snapshot_seed_skip_next_run_retries_ten_minutes()
     test_overview_adjacent_previous_with_seed_and_dual_fields()
     test_same_day_growth_baselines()
     test_growth_rate_sort_uses_prior()