refactor(install): improve modular architecture and error handling

- Remove redundant installation checks in arduino.sh, git.sh
- Add bash shell enforcement in install.sh to prevent compatibility issues
- Streamline Arduino CLI installation logic for both Arch and other systems
- Improve Git and Lazygit installation messaging consistency
- Update install usage instructions for better clarity
- Enhance shell compatibility by enforcing bash execution

install.sh

@@ -3,10 +3,15 @@
 # Archduino Install — TUI Arduino Development Environment
 # Works on both native Arch Linux and Arch/Ubuntu WSL2
 #
-# Usage: curl -kL <url> | bash
-#    or: chmod +x install.sh && ./install.sh
+# Usage: chmod +x install.sh && ./install.sh
+#    or: bash install.sh
 #
 
+# Re-exec with bash if invoked via sh/dash
+if [ -z "$BASH_VERSION" ]; then
+  exec bash "$0" "$@"
+fi
+
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 # ── Load helpers and detect environment ─────────────────────────