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/dicionario.go

@@ -72,7 +72,7 @@ func (DicionarioLoader) Load(db *sql.DB, dataDir string) error {
 		}
 
 		word := strings.ToLower(strings.TrimSpace(entry.Form.Orth))
-		if word == "" || containsDigit(word) || containsSpace(word) {
+		if word == "" || !hasLetter(word) || containsDigit(word) || containsSpace(word) {
 			continue
 		}