Admin routes: history query and CSV export

The admin History screen (ADMIN-SPEC 1g) had no API: the read
primitives existed (append-only completion-event reads, derived-state
missed logic) but nothing assembled them, so the admin PWA could not
render the event log or export it.  Feature 13's export service was
superseded by the Admin PWA and remains unimplemented by design.

Add a Home-Assistant-free core history layer (core/history.py) that
owns every rule so the two routes cannot drift: one query over the
closed due-date range [start, end] for filter all (every completion
event) / reversals (uncompleted only) / missed (DERIVED past-due open
instances via the existing completion.list_missed_for_child rule --
never stored, never appended); strict ISO date and filter validation
raising ValueError naming filter/start/end; and a csv-module serializer
with a stable documented header (ADMIN-SPEC 5 event-row fields) so the
CSV export is the SAME filtered range as the query, through one
export_history_csv call.  Admin routes GET /api/v1/admin/history and
/history.csv are thin adapters on the existing admin router (the one
require_admin dependency; no new auth check), mapping malformed input
to 422 and never 500.  completion_events stays append-only: history
only reads.

Tests (tests/test_api_admin_history.py) drive the ASGI app as an admin
via the shared JWT harness: seeded completion + reversal + past-due
open instances prove each filter's rows, the CSV header/rows via
csv.reader, due-date range scoping, 403/401 refusals, and 422s for
unknown filter, non-strict dates and inverted ranges.

api/nestquest_core.py

@@ -116,6 +116,11 @@ core_snapshot = importlib.import_module(f"{_CORE_MODULE_NAME}.snapshot")
 #: ``uncomplete_instance``) the panel's write routes call.
 core_completion = importlib.import_module(f"{_CORE_MODULE_NAME}.completion")
 
+#: The read-only history layer (``core.history.query_history``,
+#: ``export_history_csv``, ``rows_to_csv``) the admin plane's history
+#: query and CSV export routes call.
+core_history = importlib.import_module(f"{_CORE_MODULE_NAME}.history")
+
 #: The transition-event builders (``core.events.build_quest_completed_event``
 #: et al.) the panel's write routes build their SSE events with.
 core_events = importlib.import_module(f"{_CORE_MODULE_NAME}.events")
@@ -192,6 +197,7 @@ __all__ = [
     "core_dao_rules",
     "core_db",
     "core_events",
+    "core_history",
     "core_materialize",
     "core_migrations",
     "core_presence",