router: a reminder with no subject asks instead of guessing (V-383)

Slots.Text was the raw utterance for every intent, so a reminder could not
have an empty subject. StillMissing never reported SlotText, the question
"О чём напомнить?" was unaskable, and the branch in PendingQuestion.Answer
that fills a text slot could only overwrite the whole request.

The LLM path now keeps the model's own text, empty included, and the gate
turns a subjectless reminder into a question. The classifier path is
unchanged: it has no subject parser, so the utterance is the only signal it
has.

internal/router/router.go

@@ -147,7 +147,15 @@ func (r *Router) fillSlots(ctx context.Context, d *Decision, now time.Time) {
 			d.Slots.Fn, d.Slots.Args, d.Slots.HasFn = fn, args, true
 		}
 	}
-	if d.Slots.Text == "" {
+	// The extractor's Text is the raw utterance, which is the payload for a
+	// note, a query or a chat turn but not for a reminder — there Text is the
+	// subject, what she says at the hour. Backfilling it made Text impossible
+	// to be empty, so StillMissing never reported SlotText and "О чём
+	// напомнить?" was unaskable; the answer to a question she did manage to
+	// ask then overwrote the whole request instead of filling one gap
+	// (Vikunja #383). A reminder with no subject stays empty and is gated
+	// below into a question.
+	if d.Slots.Text == "" && d.Intent != IntentReminder {
 		d.Slots.Text = ex.Text
 	}
 	// Stage stays 1: it says who decided the route, and that was the LLM.
@@ -177,6 +185,12 @@ func (r *Router) gateLLMDecision(d *Decision) {
 	if d.Intent == IntentAct && !d.Slots.HasFn && d.Confidence > llmThinConfidence {
 		d.Confidence = llmThinConfidence
 	}
+	// A reminder with no subject: she knows when but not what to say then.
+	// Setting it anyway fires an empty reminder at the hour, which reads as a
+	// bug to him and cannot be repaired after the fact. Ask (Vikunja #383).
+	if d.Intent == IntentReminder && d.Slots.Text == "" && d.Confidence > llmThinConfidence {
+		d.Confidence = llmThinConfidence
+	}
 	if d.Confidence < r.threshold {
 		d.Clarify = true
 	}