Push the week's plan to Google Calendar (Feature 16)

POST /api/v1/plans/{weekStart}/push-calendar writes one event per plan
day to the chosen calendar: "Dinner: {name}" from the household dinner
time for 60 minutes in the household zone, with the dinner name,
"Start by {time}" for crock-pot dinners and the
{MEALQUEST_PUBLIC_URL}/dinner/{id} link. Event ids are the lowercase
base32hex SHA-256 of "mealquest|{weekStart}|{date}"; each event is
inserted, and a 409 updates it instead.

gcal.Service.PushEvents does the Calendar writes under the account lock,
with the same redaction as listing. plan.Service.Push records a push only
when every event was written: the plan becomes synced with
calendar_synced_at and each day stores its event id. A partial failure
records nothing; a plan edited mid-push is 409 plan_changed.

A swap, or a redraft to another dinner, clears the day's
calendar_event_id, so the next push writes just those days; a push with
none pending writes every day again.

No calendar chosen is 409 no_calendar; a deleted or read-only chosen
calendar is 409 calendar_unavailable; a refused grant is 502
reconnect_required, leaving the connection as it is.

Maestro task 5885d2b1-cf06-44ff-abf3-242d7763c3c9.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/server_test.go

@@ -202,7 +202,7 @@ func newTestPlan(t *testing.T) *plan.Service {
 	fail := func(context.Context, string, skills.WeekRequest) (skills.Week, error) {
 		return skills.Week{}, errors.New("no model in this test")
 	}
-	svc, err := plan.NewService(st, fail, runner, logger)
+	svc, err := plan.NewService(st, fail, runner, newTestGoogle(t), &url.URL{Scheme: "https", Host: "mealquest.example"}, logger)
 	if err != nil {
 		t.Fatal(err)
 	}