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>

cmd/dictimport/main.go

@@ -107,8 +107,8 @@ func main() {
 		)
 	}
 
-	// Difficulty scorer runs last, after all word data is loaded
-	loaders = append(loaders, loader.DifficultyScorer{})
+	// Prune ghost words from affix expansion, then score difficulty
+	loaders = append(loaders, loader.PruneOrphanWords{}, loader.DifficultyScorer{})
 
 	start := time.Now()
 	if err := loader.Run(db, *dataDir, loaders, skipSet); err != nil {