Ignore message edits to prevent duplicate URL previews and stat inflation

Matrix edits arrive as m.room.message with m.replace relation. Without
filtering these out, each edit was re-triggering URL previews and
incrementing user stats as if it were a new message.

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

main.go

@@ -203,6 +203,12 @@ func main() {
 			return
 		}
 
+		// Ignore edits — they arrive as m.room.message with m.replace relation.
+		// Without this check, edits re-trigger URL previews and inflate stats.
+		if content.RelatesTo != nil && content.RelatesTo.Type == event.RelReplace {
+			return
+		}
+
 		body := content.Body
 		// Strip Matrix reply fallback: "> <@user:server> ..." lines followed by blank line
 		if strings.HasPrefix(body, "> <@") || strings.HasPrefix(body, "> * <@") {