Editor: document tone, right-click word lookup, expanded stats

Four enhancements to make the editor fit real school usage:

- Per-document tone (academic/professional/casual/humorous/creative/
  persuasive/general): new documents.tone column (migration 0002), threaded
  through the docs API, a bilingual ToneSelect dropdown on the title row, and
  injected into the grammar-checkpoint LLM prompt so advice fits the register.
  The voice pass stays tone-agnostic.

- Right-click word lookup: a new offline `lexicon` package serves definitions
  (Wordset, modern ESL-friendly glosses) and synonyms (WordNet synsets first,
  then frequency+stopword-ranked Moby for breadth) from gzipped embedded data,
  behind /api/word/{word} with light morphology. The WordCard popover shows the
  definition and tappable synonym pills that swap the word in place.

- Expanded writing stats: clicking the word count opens a StatsPanel with page
  count, sentences, paragraphs, reading time, average word length, word variety,
  and Flesch-Kincaid reading level — all computed client-side.

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

internal/suggestions/handlers.go

@@ -69,8 +69,9 @@ func (h *Handler) voice(w http.ResponseWriter, r *http.Request) {
 }
 
 // pass is the signature shared by the grammar checkpoint and the voice pass:
-// given the document text it returns the model's raw suggestions.
-type pass func(ctx context.Context, client llm.LLMClient, contentText string) ([]llm.RawSuggestion, error)
+// given the document text and the document's tone it returns the model's raw
+// suggestions. The voice pass ignores tone (see llm.RunVoice).
+type pass func(ctx context.Context, client llm.LLMClient, contentText, tone string) ([]llm.RawSuggestion, error)
 
 // runPass is the shared body for both LLM passes. It loads the document text,
 // enforces the pass's per-document rate limit, runs the model, swaps in the
@@ -79,11 +80,11 @@ type pass func(ctx context.Context, client llm.LLMClient, contentText string) ([
 func (h *Handler) runPass(w http.ResponseWriter, r *http.Request, limiter *llm.RateLimiter, run pass, scope pendingScope) {
 	docID := chi.URLParam(r, "id")
 
-	var contentText string
+	var contentText, tone string
 	err := h.DB.QueryRow(
-		`SELECT content_text FROM documents WHERE id = ? AND user_id = ?`,
+		`SELECT content_text, tone FROM documents WHERE id = ? AND user_id = ?`,
 		docID, db.LocalUserID,
-	).Scan(&contentText)
+	).Scan(&contentText, &tone)
 	if errors.Is(err, sql.ErrNoRows) {
 		errorJSON(w, http.StatusNotFound, "document not found")
 		return
@@ -111,7 +112,7 @@ func (h *Handler) runPass(w http.ResponseWriter, r *http.Request, limiter *llm.R
 		return
 	}
 
-	raw, err := run(r.Context(), h.Client, contentText)
+	raw, err := run(r.Context(), h.Client, contentText, tone)
 	if err != nil {
 		errorJSON(w, http.StatusBadGateway, "llm pass failed: "+err.Error())
 		return