Stamps round on every effect.* wire message

[johnnyt]

Propagates the engine's round counter onto the nine effect.* wire
types that still emitted a nil round envelope; effect.budget_exhausted
already carried it. The value is the engine's own stamp (statifier
ADR-0046, st-xb2b), carried verbatim by the normalizer - nothing is
invented on the wire.

Wire-format decisions recorded (this repo owns the wire format):

• Additive envelope field under the must-ignore rule, so the format
  version stays 1 - the same reasoning effect.datamodel_change recorded
  for adding a whole type (sui-h92 precedent). Consumers of older
  recorded streams must still tolerate effect.* messages without the
  key.
• Repoints docs/wire-format.md's forward references from sui-t36.5
  (which shipped without this propagation) to sui-67d.
• Reconciles the st-xb2b vs st-nbmj citation: st-nbmj filed the
  upstream gap and was superseded by st-xb2b, whose ADR-0046 decided
  it; the References entry now says so instead of attributing ADR-0046
  to both.

Interaction with the datamodel explorer (PR #32, merged mid-flight):
effect.datamodel_change no longer carries a nil round envelope - it
now carries the engine's stamp. lib/statifier_ui/datamodel_explorer/*
is behaviorally unaffected: it orders writes by
{macrostep, microstep, seq} and never reads the round field. Its
moduledoc's "finer marking would need an upstream wire change" note was
stale the moment this landed, so it now records that round-granular
change marking is a possible local refinement, while the pane
deliberately stays at macrostep granularity.

EventLog needed no code change, as sui-t36.5 planned: its
round-presence routing now files round-carrying effect.* messages into
their round buckets; a new test pins that, and the round-less case
remains covered as the older-recorded-stream shape.

Full mix quality gate green on top of current main (412 tests,
93.2% coverage, dialyzer clean).

Closes: sui-67d