reminders: store what she says, show it in his clock (V-469)

Two of the four defects on the task.

The stored payload was the whole utterance, so /reminders and the agenda
recited "напомни завтра в 9 утра выпить таблетки" where the reminder is
"выпить таблетки". The marker is an instruction that was already carried out
and the hour is already a column, so reminderBody strips both, and falls back
to the unstripped body whenever stripping would leave nothing — a reminder
that fires and says nothing is worse than a wordy one.

The page rendered the raw {"text":...} envelope and the UTC instant. Both are
now done in mavweb: reminderRows unwraps the payload and formats through
Local(). The unwrap is a copy of store.ReminderText rather than a call to it,
because mavweb builds without CGO and internal/store carries the sqlite
driver — the ipc DTOs are decoupled from the store on purpose.

TestClarifySubjectAnswerFillsRatherThanClobbers asserted the hour survived as
a word in the payload. It now asserts the fire time, which is where the hour
lives.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

cmd/mavend/clarify_test.go

@@ -497,8 +497,12 @@ func TestClarifySubjectAnswerFillsRatherThanClobbers(t *testing.T) {
 	if !strings.Contains(reminders[0].Payload, "маме") {
 		t.Fatalf("the answer never reached the reminder: %q", reminders[0].Payload)
 	}
-	if !strings.Contains(reminders[0].Payload, "11") {
-		t.Fatalf("the answer clobbered the original request: %q", reminders[0].Payload)
+	// The hour is the fire time, not a word in the body: the body is what she
+	// says at the hour, and the time expression is stripped out of it
+	// (Vikunja #469). Clobbering the parked request would show up here as a
+	// reminder that fires at some other time than the one he asked for.
+	if got := reminders[0].FireTs.UTC(); !got.Equal(at.UTC()) {
+		t.Fatalf("the answer clobbered the original request: fires at %v, want %v", got, at.UTC())
 	}
 }