Move RYMCU BigSmart under manufacturer directory

Create main/boards/rymcu/bigsmart so future RYMCU boards can live under the same manufacturer directory. Update CMake to set MANUFACTURER to rymcu while preserving BOARD_NAME as rymcu-bigsmart, and adjust config.json so release output remains rymcu-bigsmart.

main/boards/rymcu/bigsmart/config.json

@@ -1,8 +1,9 @@
 {
+    "manufacturer": "rymcu",
     "target": "esp32s3",
     "builds": [
         {
-            "name": "rymcu-bigsmart",
+            "name": "bigsmart",
             "sdkconfig_append": [
                 "CONFIG_USE_DEVICE_AEC=y"
             ]