P4: schedule battery — generic cron Runner

A host-agnostic ticker (Tick = one pass; Loop = run on an interval until ctx
done) that fires due jobs. Every dependency is wired by the host:
- Due lists due jobs (skill.ListDueScheduled / persona.ListScheduledAgents),
- Run executes one (run.Executor),
- Mark stamps the next fire (store.MarkScheduledRun),
- Next computes the cron next-fire (a cron lib / skill's parser).

The battery owns NO cron grammar, so it never duplicates the parser. A job whose
Run or Next errors is logged and left un-stamped (stays due, retries next tick)
— one bad job can't stall the others; only a failing Due lister is pass-fatal.

Tests: due jobs run + stamped, bad-cron job runs but isn't stamped, a failing
Run doesn't stamp or stall siblings, Due error surfaces. Core imports ZERO.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -70,7 +70,8 @@ BATTERIES (opt-in siblings, each nil-safe + a default):
   audit/     run.Audit Sink + Writer + queryable Memory  [P4 ✓]
              default (skillaudit Storage iface; GORM stays in mort)
   critic/    two-tier timeout state machine + Escalator  [P4]
-  schedule/  cron runner cores                           [P4]
+  schedule/  generic cron Runner (Tick/Loop over a wired  [P4 ✓]
+             Due/Run/Mark/Next; no cron grammar of its own)
   checkpoint/ CheckpointStore + run.Checkpointer handle  [P4 ✓]
              (throttled Save/Complete/Fail) + Memory (exec wiring=P2 follow-up)
   budget/    DBBudget rolling-7d + NoOp (run.Budget);    [P4 ✓]