Add Phase 2+3 features: antonyms, backing, pronunciation, etymology, difficulty, affix expansion

New endpoints: /antonyms, /backing, /pronunciation, /etymology with difficulty
scoring on /random. Cross-language synset backing links French/Portuguese words
to English equivalents via WordNet 3.0 synset IDs (matching WOLF and OMW offsets).

New loaders: Hunspell affix expansion (fr, pt-PT), English programmatic inflector,
CMU Pronouncing Dictionary, SUBTLEX-US frequency, CETEMPúblico frequency,
Open Multilingual Wordnet (Portuguese), and SQL-based difficulty scoring.

Schema v2 adds tables: antonyms, synsets, word_synsets, pronunciations, etymology
with migration support for existing databases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/loader/cmudict.go

@@ -0,0 +1,114 @@
+package loader
+
+import (
+	"bufio"
+	"database/sql"
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// CMUDictLoader loads pronunciation data from the CMU Pronouncing Dictionary.
+// Format: WORD  P1 P2 P3 (two-space separated word and phonemes)
+// Coverage: English only (~134,000 entries).
+type CMUDictLoader struct{}
+
+func (CMUDictLoader) Name() string { return "cmudict" }
+
+func (CMUDictLoader) Load(db *sql.DB, dataDir string) error {
+	candidates := []string{
+		filepath.Join(dataDir, "cmudict-0.7b"),
+		filepath.Join(dataDir, "cmudict.dict"),
+		filepath.Join(dataDir, "cmudict"),
+	}
+
+	var path string
+	for _, c := range candidates {
+		if _, err := os.Stat(c); err == nil {
+			path = c
+			break
+		}
+	}
+	if path == "" {
+		slog.Warn("cmudict: no data file found, skipping", "searched", candidates)
+		return nil
+	}
+
+	f, err := os.Open(path)
+	if err != nil {
+		return fmt.Errorf("cmudict: open: %w", err)
+	}
+	defer f.Close()
+
+	tx, err := db.Begin()
+	if err != nil {
+		return fmt.Errorf("cmudict: begin tx: %w", err)
+	}
+	defer tx.Rollback()
+
+	stmt, err := tx.Prepare(`
+		INSERT OR IGNORE INTO pronunciations (word_id, format, value, source)
+		SELECT id, 'cmu', ?, 'cmudict' FROM words WHERE word = ? AND lang = 'en'`)
+	if err != nil {
+		return fmt.Errorf("cmudict: prepare: %w", err)
+	}
+	defer stmt.Close()
+
+	scanner := bufio.NewScanner(f)
+	var count int
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" || strings.HasPrefix(line, ";;;") {
+			continue
+		}
+
+		// Format: "WORD  PH1 PH2 PH3" (two spaces between word and phonemes)
+		// Some entries have variant markers like "WORD(2)  PH1 PH2"
+		parts := strings.SplitN(line, "  ", 2)
+		if len(parts) != 2 {
+			// Try single space (some versions)
+			idx := strings.IndexByte(line, ' ')
+			if idx == -1 {
+				continue
+			}
+			parts = []string{line[:idx], strings.TrimSpace(line[idx+1:])}
+		}
+
+		word := strings.ToLower(strings.TrimSpace(parts[0]))
+		phonemes := strings.TrimSpace(parts[1])
+
+		if word == "" || phonemes == "" {
+			continue
+		}
+
+		// Skip variant entries like "WORD(2)" — keep only primary pronunciation
+		if strings.Contains(word, "(") {
+			continue
+		}
+
+		if containsDigit(word) || containsSpace(word) {
+			continue
+		}
+
+		res, err := stmt.Exec(phonemes, word)
+		if err != nil {
+			return fmt.Errorf("cmudict: insert: %w", err)
+		}
+		if n, _ := res.RowsAffected(); n > 0 {
+			count++
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("cmudict: scan: %w", err)
+	}
+
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("cmudict: commit: %w", err)
+	}
+	slog.Info("cmudict loaded", "pronunciations", count)
+	return nil
+}