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/docs/handlers.go

@@ -81,11 +81,11 @@ func (h *Handler) create(w http.ResponseWriter, r *http.Request) {
 	var doc db.Document
 	err := h.DB.QueryRow(
 		`INSERT INTO documents (user_id) VALUES (?)
-		 RETURNING id, user_id, title, content, content_text, word_count, created_at, updated_at`,
+		 RETURNING id, user_id, title, content, content_text, tone, word_count, created_at, updated_at`,
 		db.LocalUserID,
 	).Scan(
 		&doc.ID, &doc.UserID, &doc.Title, &doc.Content, &doc.ContentText,
-		&doc.WordCount, &doc.CreatedAt, &doc.UpdatedAt,
+		&doc.Tone, &doc.WordCount, &doc.CreatedAt, &doc.UpdatedAt,
 	)
 	if err != nil {
 		serverError(w, err)
@@ -115,6 +115,7 @@ type updateRequest struct {
 	Title       *string `json:"title"`
 	Content     *string `json:"content"`
 	ContentText *string `json:"content_text"`
+	Tone        *string `json:"tone"`
 	WordCount   *int    `json:"word_count"`
 }
 
@@ -134,10 +135,11 @@ func (h *Handler) update(w http.ResponseWriter, r *http.Request) {
 		    SET title        = COALESCE(?, title),
 		        content      = COALESCE(?, content),
 		        content_text = COALESCE(?, content_text),
+		        tone         = COALESCE(?, tone),
 		        word_count   = COALESCE(?, word_count),
 		        updated_at   = CURRENT_TIMESTAMP
 		  WHERE id = ? AND user_id = ?`,
-		req.Title, req.Content, req.ContentText, req.WordCount, id, db.LocalUserID,
+		req.Title, req.Content, req.ContentText, req.Tone, req.WordCount, id, db.LocalUserID,
 	)
 	if err != nil {
 		serverError(w, err)
@@ -177,13 +179,13 @@ func (h *Handler) delete(w http.ResponseWriter, r *http.Request) {
 func (h *Handler) fetch(id string) (db.Document, error) {
 	var doc db.Document
 	err := h.DB.QueryRow(
-		`SELECT id, user_id, title, content, content_text, word_count, created_at, updated_at
+		`SELECT id, user_id, title, content, content_text, tone, word_count, created_at, updated_at
 		   FROM documents
 		  WHERE id = ? AND user_id = ?`,
 		id, db.LocalUserID,
 	).Scan(
 		&doc.ID, &doc.UserID, &doc.Title, &doc.Content, &doc.ContentText,
-		&doc.WordCount, &doc.CreatedAt, &doc.UpdatedAt,
+		&doc.Tone, &doc.WordCount, &doc.CreatedAt, &doc.UpdatedAt,
 	)
 	return doc, err
 }