Prune ghost words from affix expansion and stop frequency loader creating words

- Add PruneOrphanWords post-import step that deletes words with no
  definitions, synonyms, translations, pronunciations, etymology,
  synsets, or frequency data
- Remove INSERT path from CETEMPublico loader — frequency data should
  annotate existing words, not create new ones (was inflating pt-PT
  from 136K real words to 718K)
- Add hasLetter filter to hunspell, affix, and dicionario loaders to
  block punctuation entries like ".", ",", "(" from entering the DB
- Move hasLetter helper to scowl.go alongside other shared filters

Impact: en 655K→129K, pt-PT 1.5M→136K, fr 80K→56K (on reimport)

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

internal/loader/affix.go

@@ -48,7 +48,7 @@ func (a AffixLoader) Load(db *sql.DB, dataDir string) error {
 	seen := make(map[string]struct{})
 	for _, entry := range dicEntries {
 		for _, form := range expandWord(entry.word, entry.flags, rules) {
-			if containsDigit(form) || containsSpace(form) {
+			if !hasLetter(form) || containsDigit(form) || containsSpace(form) {
 				continue
 			}
 			if _, dup := seen[form]; dup {