Remove Isaac-GR00T submodule and update gitignore

- Remove Isaac-GR00T submodule from git tracking
- Add Isaac-GR00T/, install/, log/ to .gitignore
- Keep physical directory for local use but exclude from version control

Author: Seongoo

.gitignore

@@ -709,6 +709,13 @@ CATKIN_IGNORE
 AMENT_IGNORE
 COLCON_IGNORE
 
+## Build and install directories
+install/
+log/
+
+## Submodule directories (not tracked)
+Isaac-GR00T/
+
 
 ##############################
 # ETC.