Add full-text search indexing for word tokens and update tokenization logic

- Introduced word index (`WordPrefix`) for tokenized search terms.
- Added word token extraction in event and filter processing.
- Implemented Unicode-aware, case-insensitive tokenizer with URL, mention, and hex filters.
- Extended full-text indexing to include tags and content.

app/handle-relayinfo.go

@@ -46,6 +46,7 @@ func (s *Server) HandleRelayInfo(w http.ResponseWriter, r *http.Request) {
 		relayinfo.ExpirationTimestamp,
 		relayinfo.ProtectedEvents,
 		relayinfo.RelayListMetadata,
+		relayinfo.SearchCapability,
 	)
 	if s.Config.ACLMode != "none" {
 		supportedNIPs = relayinfo.GetList(
@@ -62,6 +63,7 @@ func (s *Server) HandleRelayInfo(w http.ResponseWriter, r *http.Request) {
 			relayinfo.ExpirationTimestamp,
 			relayinfo.ProtectedEvents,
 			relayinfo.RelayListMetadata,
+			relayinfo.SearchCapability,
 		)
 	}
 	sort.Sort(supportedNIPs)