fix(room): invert use_exact logic so it controls all-message mode

Previously: use_exact=false → respond to all messages (wrong default)
Now: use_exact=true → respond to all messages; use_exact=false → only @ai

libs/room/src/service/mod.rs

@@ -265,7 +265,7 @@ impl RoomService {
             None => return Ok(false),
         };
 
-        if !config.use_exact {
+        if config.use_exact {
             return Ok(true);
         }