Add regional variant tagging (us/gb) for English words

- SCOWL loader now loads american-words and british-words alongside
  english-words, tagging each with variant "us", "gb", or NULL (common)
- Words appearing in both American and British lists get NULL variant
- Add variant column to words table with schema migration
- API: /define returns variant field for English, /random and /words
  accept ?variant=us|gb filter
- Add total word count to server status line
- Fix rows.Close leak in PopulateCMUTails, add rows.Err() check
- Add tests for PopulateCMUTails, cmuTail, TotalWordCount
- Expand test seed data and assertions to cover pt-PT definitions,
  synonyms, and validity checks
- Update README with variant docs, /difficulty, /words, /rhyme
  endpoints, and current database statistics

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

internal/loader/scowl.go

@@ -31,35 +31,61 @@ var scowlFrequency = map[int]int{
 }
 
 type scowlFile struct {
-	path string
-	size int
+	path    string
+	size    int
+	variant string // "us", "gb", or "" for common English
 }
 
 func (SCOWLLoader) Load(db *sql.DB, dataDir string) error {
-	pattern := filepath.Join(dataDir, "scowl", "final", "english-words.*")
-	files, err := filepath.Glob(pattern)
-	if err != nil {
-		return fmt.Errorf("scowl: glob: %w", err)
+	type prefixVariant struct {
+		prefix  string
+		variant string
 	}
-	if len(files) == 0 {
-		return fmt.Errorf("scowl: no files matching %s", pattern)
+	prefixes := []prefixVariant{
+		{"english-words", ""},
+		{"american-words", "us"},
+		{"british-words", "gb"},
 	}
 
-	// Filter to sizes <= 70 and track the tier
+	var allFiles []string
+	for _, pv := range prefixes {
+		pattern := filepath.Join(dataDir, "scowl", "final", pv.prefix+".*")
+		matches, err := filepath.Glob(pattern)
+		if err != nil {
+			return fmt.Errorf("scowl: glob: %w", err)
+		}
+		allFiles = append(allFiles, matches...)
+	}
+	if len(allFiles) == 0 {
+		return fmt.Errorf("scowl: no word files found in %s", filepath.Join(dataDir, "scowl", "final"))
+	}
+
+	// Build a map from prefix to variant for quick lookup
+	prefixToVariant := make(map[string]string)
+	for _, pv := range prefixes {
+		prefixToVariant[pv.prefix] = pv.variant
+	}
+
+	// Filter to sizes <= 70 and track the tier + variant
 	var selected []scowlFile
-	for _, f := range files {
+	for _, f := range allFiles {
 		base := filepath.Base(f)
-		// Files are like english-words.10, english-words.20, etc.
+		// Files are like english-words.10, american-words.35, etc.
 		parts := strings.SplitN(base, ".", 2)
 		if len(parts) != 2 {
 			continue
 		}
+		prefix := parts[0]
+		variant, ok := prefixToVariant[prefix]
+		if !ok {
+			continue
+		}
 		var size int
 		if _, err := fmt.Sscanf(parts[1], "%d", &size); err != nil {
 			continue
 		}
 		if size <= 70 {
-			selected = append(selected, scowlFile{path: f, size: size})
+			selected = append(selected, scowlFile{path: f, size: size, variant: variant})
 		}
 	}
 
@@ -69,8 +95,15 @@ func (SCOWLLoader) Load(db *sql.DB, dataDir string) error {
 	}
 	defer tx.Rollback()
 
-	stmt, err := tx.Prepare(`INSERT INTO words (word, lang, frequency) VALUES (?, 'en', ?)
-		ON CONFLICT(word, lang) DO UPDATE SET frequency = MAX(frequency, excluded.frequency)`)
+	stmt, err := tx.Prepare(`INSERT INTO words (word, lang, frequency, variant) VALUES (?, 'en', ?, ?)
+		ON CONFLICT(word, lang) DO UPDATE SET
+			frequency = MAX(frequency, excluded.frequency),
+			variant = CASE
+				WHEN words.variant IS NULL THEN excluded.variant
+				WHEN excluded.variant IS NULL THEN words.variant
+				WHEN words.variant = excluded.variant THEN words.variant
+				ELSE NULL
+			END`)
 	if err != nil {
 		return fmt.Errorf("scowl: prepare: %w", err)
 	}
@@ -79,7 +112,7 @@ func (SCOWLLoader) Load(db *sql.DB, dataDir string) error {
 	var count int
 	for _, sf := range selected {
 		freq := scowlFrequency[sf.size]
-		n, err := loadSCOWLFile(stmt, sf.path, freq)
+		n, err := loadSCOWLFile(stmt, sf.path, freq, sf.variant)
 		if err != nil {
 			return fmt.Errorf("scowl: load %s: %w", sf.path, err)
 		}
@@ -93,13 +126,19 @@ func (SCOWLLoader) Load(db *sql.DB, dataDir string) error {
 	return nil
 }
 
-func loadSCOWLFile(stmt *sql.Stmt, path string, freq int) (int, error) {
+func loadSCOWLFile(stmt *sql.Stmt, path string, freq int, variant string) (int, error) {
 	f, err := os.Open(path)
 	if err != nil {
 		return 0, err
 	}
 	defer f.Close()
 
+	// Convert empty variant to SQL NULL
+	var variantParam any
+	if variant != "" {
+		variantParam = variant
+	}
+
 	var count int
 	scanner := bufio.NewScanner(f)
 	for scanner.Scan() {
@@ -111,7 +150,7 @@ func loadSCOWLFile(stmt *sql.Stmt, path string, freq int) (int, error) {
 		if containsAny(word, " ", "'", "-") || containsDigit(word) {
 			continue
 		}
-		if _, err := stmt.Exec(word, freq); err != nil {
+		if _, err := stmt.Exec(word, freq, variantParam); err != nil {
 			return 0, err
 		}
 		count++