Phase 9: ESL superpowers — Chinese gloss + tone-rewrite

Inline Chinese gloss (offline) and a "say it more naturally" / tone-rewrite,
the two ESL features for the Mandarin-speaking writer.

Gloss: embedded English→Chinese dictionary (gloss.json.gz, 57k common words
built from ECDICT via scripts/build_gloss.py). lexicon gains Gloss()/Result.Gloss
and a lightweight GET /api/gloss/{word}; the right-click WordCard leads with the
中文; GlossTip shows it on a 350ms hover (reuses wordAt, so CJK is never glossed).
Offline + instant, works with the LLM down.

Rewrite: selecting text pops a SelectionBubble (✨更自然 + the tone vocabulary);
picking a style calls POST /api/docs/:id/rewrite (llm.RunRewrite, stateless,
owner-scoped) and shows a RewritePreview (original→rewrite, accept/cancel/retry).
Accept applies it in-editor.

Tests added in lexicon and suggestions. go build/vet/test, tsc, vite all clean;
live smoke vs a fake vLLM verified gloss + rewrite + 400/404/502 paths.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

internal/lexicon/handlers.go

@@ -25,6 +25,15 @@ func (h *Handler) Routes() chi.Router {
 	return r
 }
 
+// GlossRoutes returns the router mounted at /api/gloss — the lightweight
+// Chinese-only lookup behind the inline hover/select gloss. It shares the
+// Handler's Lexicon, so the datasets still load just once.
+func (h *Handler) GlossRoutes() chi.Router {
+	r := chi.NewRouter()
+	r.Get("/{word}", h.gloss)
+	return r
+}
+
 // lookup returns the definition + synonyms for one word. A word found in neither
 // dataset still returns 200 with empty lists, so the popover can show a friendly
 // "nothing found" rather than an error state.
@@ -48,3 +57,25 @@ func (h *Handler) lookup(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Cache-Control", "public, max-age=86400")
 	_ = json.NewEncoder(w).Encode(res)
 }
+
+// gloss returns just the Chinese translation for one word. Like lookup, a miss
+// is a 200 with an empty gloss so the hover tooltip can quietly skip rather than
+// error.
+func (h *Handler) gloss(w http.ResponseWriter, r *http.Request) {
+	word := chi.URLParam(r, "word")
+	if decoded, err := url.PathUnescape(word); err == nil {
+		word = decoded
+	}
+
+	res, err := h.Lex.Gloss(word)
+	if err != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusInternalServerError)
+		_ = json.NewEncoder(w).Encode(map[string]string{"error": err.Error()})
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Cache-Control", "public, max-age=86400")
+	_ = json.NewEncoder(w).Encode(res)
+}