SSE: publish uncompleted, child-day-complete and missed transitions

The panel stream so far carried only quest-completed. This adds the
three remaining documented transitions (§3) so the panel UI can react
to reversals, full days, and nightly misses through the same ONE
publisher:

- core/events.py gains build_quest_missed_event, mirroring the
  sweep's hand-built payload exactly (shared _instance_payload shape),
  so the API plane publishes the same shape the integration sweep fires.
- api/transitions.py adds the reusable publish helpers the later
  uncomplete route (da0226b3) and the API-side missed sweep will call;
  payloads are always built by the core builders, never hand-built.
- The panel complete route now evaluates the day-complete rule on an
  actual transition, off the completed event's payload and the route's
  single clock read; the core builder still decides, so a zero-quest
  day and a non-today instance never fire it and a no-op re-complete
  publishes nothing.
- Tests drive all three transitions through the real SSE stream
  (server-loop scheduling for the not-yet-routed helpers) and assert
  every documented payload field.

api/transitions.py

@@ -0,0 +1,83 @@
+"""Reusable SSE transition publishers for the API service (task 44c93cfd).
+
+Each helper wraps the ONE publisher on ``app.state.publisher`` with a
+single documented transition: it builds the payload through the core
+event builders (``nestquest_core.events``) — never hand-built here —
+and fans it out with :meth:`~api.events.TransitionPublisher.publish`.
+
+The uncomplete route (follow-up task da0226b3) and the API-side missed
+sweep do not exist yet; these helpers are the functions they will call,
+and the SSE tests exercise them directly.  Fan-out stays fire-and-forget
+(see api/events.py): a slow subscriber drops the event and recovers by
+polling the snapshot.
+"""
+from __future__ import annotations
+
+import datetime
+
+from api.nestquest_core import core_events
+
+
+async def publish_quest_uncompleted(
+    database: object, instance_id: int, publisher: object
+) -> None:
+    """Publish ONE ``nestquest_quest_uncompleted`` event for an actual
+    reversal of ``instance_id``.
+
+    The payload is built by the core builder
+    (:func:`nestquest_core.events.build_quest_uncompleted_events`);
+    this helper only picks the single event out of the builder's list
+    and publishes it.
+    """
+    events = await core_events.build_quest_uncompleted_events(
+        database, instance_id
+    )
+    for event_type, payload in events:
+        publisher.publish(event_type, payload)
+
+
+async def publish_quest_missed(
+    database: object, instance_id: int, publisher: object
+) -> None:
+    """Publish ONE ``nestquest_quest_missed`` event for ``instance_id``.
+
+    The payload is built by the core builder
+    (:func:`nestquest_core.events.build_quest_missed_event`), which
+    mirrors the documented sweep payload exactly (§3 of
+    design/ENTITIES-AND-SERVICES.md).
+    """
+    event_type, payload = await core_events.build_quest_missed_event(
+        database, instance_id
+    )
+    publisher.publish(event_type, payload)
+
+
+async def publish_child_day_complete(
+    database: object,
+    completed_payload: dict,
+    today: datetime.date,
+    publisher: object,
+) -> bool:
+    """Publish ``nestquest_child_day_complete`` when a completion
+    cleared the child's whole day; return whether one was published.
+
+    The day-complete rule lives entirely in the core builder
+    (:func:`nestquest_core.events.build_child_day_complete_event`):
+    it returns ``None`` when the day did not clear (a zero-quest day
+    or a non-today instance) and this helper publishes nothing then.
+    """
+    event = await core_events.build_child_day_complete_event(
+        database, completed_payload, today=today
+    )
+    if event is None:
+        return False
+    event_type, payload = event
+    publisher.publish(event_type, payload)
+    return True
+
+
+__all__ = [
+    "publish_child_day_complete",
+    "publish_quest_missed",
+    "publish_quest_uncompleted",
+]