feat(p1): add daily snapshots and fan tracking

Implement P1: seven-metric view snapshots, relation/stat fan snapshots, failure placeholders, resume by daily completion markers, Cookie login warnings, daily SQLite backups, Shanghai daily scheduling, and CLI snapshot/auth-check commands. Real read-only run captured 795/795 videos successfully over 1124s with a verified daily backup.

reaction_board/scheduler.py

@@ -18,6 +18,7 @@ class ScheduledTask:
     interval: float
     fn: Callable[[], Any]
     next_run: float = 0.0
+    next_run_fn: Callable[[float], float] | None = None
 
 
 @dataclass
@@ -77,7 +78,10 @@ class Scheduler:
             else:
                 self._log("info", "scheduler.task_ok", task=task.name)
             finished = self._clock()
-            task.next_run = started + task.interval
+            if task.next_run_fn is not None:
+                task.next_run = task.next_run_fn(started)
+            else:
+                task.next_run = started + task.interval
             result = TaskResult(
                 name=task.name,
                 started_at=started,