test(fuzz): the replay fuzzer writes invoice.written_off

S7 added the event type (R-B step 6: the fuzzer's list must name every
type the store replays, the_replay_fuzzer_writes_every_event_type) and
the merge lost the line; the S7 gate on main caught it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

fuzz/fuzz_targets/fuzz_store_replay.rs

@@ -28,6 +28,7 @@ const TYPES: &[&str] = &[
     "customer.added", "document.filed", "entry.created", "entry.line_added",
     "entry.line_class_set", "entry.posted", "entry.reversed", "entry.vendor_set",
     "fx.rate_set", "invoice.created", "invoice.payment_received", "invoice.sent",
+    "invoice.written_off",
     "journal.tail_repaired",
     "line.cleared", "payroll.run", "period.closed", "period.created", "receipt.attached",
     "receipt.linked", "receipt.unlinked", "recurring.generated", "recurring.registered",