fix: setup.sh and install.sh improvements (#155)

- setup.sh: Skip git init if .git already exists (prevents errors in existing repos)
- install.sh: Copy setup.sh directly instead of hardcoding a simplified version
  This ensures global installation uses the same setup logic as local,
  including .ralphrc generation via enable_core.sh

Co-authored-by: dawenrenhub <darwinren321@gmail.com>

setup.sh

@@ -92,8 +92,10 @@ CB_OUTPUT_DECLINE_THRESHOLD=70
 RALPHRCEOF
 fi
 
-# Initialize git
-git init
+# Initialize git (skip if already initialized)
+if [[ ! -d ".git" ]]; then
+    git init
+fi
 echo "# $PROJECT_NAME" > README.md
 git add .
 git commit -m "Initial Ralph project setup"