fix(cassettes): break the same-second tie with the machine's counter

The ordering gate compares created_at, which NIP-01 defines at one-second
granularity. A dispense and the publish that follows it land inside one
second routinely, so the report was dropped and the operator kept the
pre-dispense count until the next heartbeat five minutes later.

The machine bumps a counter on every local change to a bay count and
carries it in its state document. m015 stores it per row, and the gate
consults it only when the stamps are equal, where created_at carries no
information at all.

Only on equality, deliberately. A machine whose state.db was replaced
restarts its counter at zero while its wall clock keeps moving forward;
gating on the counter across different stamps would lock that machine out
for good. Equal stamps with no counter on either side stay closed, which
costs one heartbeat and risks nothing.

models.py

@@ -677,6 +677,9 @@ class CassetteConfig(BaseModel):
     state_count: int | None
     state_at: datetime | None
     state_event_id: str | None
+    # The machine's own counter, bumped on every local count change. Breaks a
+    # same-second tie in the ordering gate, where created_at cannot.
+    state_seq: int | None = None
 
 
 class CassettePayloadRow(BaseModel):