Make the dictionary startup line report rows, not capabilities

It logged dictionary.Langs(), which is a compile-time constant of the languages
DreamDict *supports*. The database deployed until today supported Spanish and
contained none of it, so the line printed a confident "[en fr pt-PT es zh]"
over a file where every Spanish lookup came back empty — the exact failure the
line exists to catch, reported as success.

Contents() counts rows per language instead. For a file somebody has to copy
onto the box by hand, "what is in it" is the only question worth asking, and
the answer is now en=136615 es=102971 fr=56096 pt-PT=136300 zh=120883.

Claude-Session: https://claude.ai/code/session_016y6gyuHkQXPiEuW8RGQyua

cmd/server/main.go

@@ -96,7 +96,7 @@ func main() {
 	defer dict.Close()
 	lexSet := lexicon.NewSet(dict)
 	if lexSet.HasDreamDict() {
-		log.Printf("dictionary: DreamDict open at %s (%v)", cfg.DictPath, dict.Langs())
+		log.Printf("dictionary: DreamDict open at %s (%s)", cfg.DictPath, lexSet.Contents())
 	} else {
 		log.Printf("dictionary: no dict.db at %s — English/Chinese only", cfg.DictPath)
 	}