reminders: confirm from the row, not from the sentence (V-507)

The confirmation was phrased by the replier off Slots.Text, so it named
whatever hour the utterance contained — including one the parser rejected
or read differently. He heard 'напомню в семь' with no row at seven, and
stopped thinking about it.

actionReminder now phrases it itself from the stored fire time, so the
sentence and the row cannot disagree. Deterministic: the one sentence that
must match a database row is not one to hand to a 1.7B.

Also fixes formatTime, which had t.Format("2 января") — Go reads that as a
literal, so every fact older than a day read as January. The month comes
from internal/lexicon now, which is where months live.

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

cmd/mavend/actions_reminder.go

@@ -2,8 +2,11 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"log"
+	"time"
 
+	"github.com/kami/maven/internal/lexicon"
 	"github.com/kami/maven/internal/phraser"
 	"github.com/kami/maven/internal/router"
 )
@@ -33,5 +36,24 @@ func (h *reactiveHandler) actionReminder(ctx context.Context, dec router.Decisio
 		log.Printf("voice: create reminder: %v", err)
 		return phraser.Ack(phraser.FailReminder, nil)
 	}
-	return ""
+	// Phrased from the row, never from the utterance (Vikunja #507). The
+	// replier only ever saw Slots.Text, so it named whatever hour the sentence
+	// contained — including one the parser had rejected or read differently.
+	// A confirmation naming an hour no row holds is worse than a clarify,
+	// because he stops thinking about it.
+	return reminderConfirm(dec.Slots.Time, h.now())
+}
+
+// reminderConfirm — the confirmation for a reminder that exists, naming the
+// stored fire time. Deterministic on purpose: the one sentence that must match
+// a database row is not one to hand to a 1.7B.
+func reminderConfirm(fire, now time.Time) string {
+	when := dayPrefix(now, fire)
+	if when == "это" {
+		// Further out than the day words reach — say the date instead of a
+		// word that would be wrong.
+		date := fmt.Sprintf("%d %s", fire.Day(), lexicon.MonthGenitive(int(fire.Month())))
+		return "хорошо, напомню " + date + " в " + fire.Format("15:04") + "."
+	}
+	return "хорошо, напомню " + when + " в " + fire.Format("15:04") + "."
 }