Embed a question and a stored note differently (Vikunja #371)

Note recall is asymmetric: a short question goes in, a longer note comes
out. Adds EmbedQuery/EmbedPassage helpers and the e5 prefixes, and points
the note/fact write path at the passage side and the query path at the
query side. Reviewers: the three call sites in voice.go.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

cmd/mavend/voice.go

@@ -567,7 +567,7 @@ func (h *reactiveHandler) applyAction(ctx context.Context, dec router.Decision)
 		// fail the fact write). Facts aren't in the notes table, so this is the
 		// only recall path for them — "когда я пил воду?" reads back from here.
 		if h.memStore != nil {
-			if vec, err := h.embedder.Embed(ctx, dec.Utterance); err != nil {
+			if vec, err := router.EmbedPassage(ctx, h.embedder, dec.Utterance); err != nil {
 				log.Printf("voice: embed fact for memory: %v", err)
 			} else if err := h.memStore.Insert(ctx, "fact:"+dec.Slots.Key+":"+strconv.FormatInt(now.Unix(), 10), vec, map[string]string{
 				"source": "voice",
@@ -681,7 +681,7 @@ func (h *reactiveHandler) applyAction(ctx context.Context, dec router.Decision)
 		// embed the note text with the same model the classifier uses, persist
 		// via CoreAPI (source=tap:voice). Semantic recall lives in `notes`, not
 		// facts — no predicate reads it (spec's two-memory split).
-		vec, err := h.embedder.Embed(ctx, dec.Utterance)
+		vec, err := router.EmbedPassage(ctx, h.embedder, dec.Utterance)
 		if err != nil {
 			log.Printf("voice: embed note: %v", err)
 			return "не получилось сохранить заметку."
@@ -758,7 +758,7 @@ func (h *reactiveHandler) applyAction(ctx context.Context, dec router.Decision)
 			return fmt.Sprintf("в %s сейчас %.0f градусов, %s.", w.Location, w.Temperature, w.Condition)
 		}
 
-		vec, err := h.embedder.Embed(ctx, dec.Utterance)
+		vec, err := router.EmbedQuery(ctx, h.embedder, dec.Utterance)
 		if err != nil {
 			log.Printf("voice: embed query: %v", err)
 			return "не получилось найти ответ."