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

lib/git.sh

@@ -3,18 +3,17 @@
 
 step "8/9 — Setting up Git + Lazygit"
 
-if ! command -v lazygit &>/dev/null; then
-  if $IS_ARCH; then
-    $PKG_INSTALL lazygit
-  else
-    LAZYGIT_VERSION=$(curl -ks "https://api.github.com/repos/jesseduffield/lazygit/releases/latest" | jq -r '.tag_name' | sed 's/v//')
-    curl -kLo /tmp/lazygit.tar.gz "https://github.com/jesseduffield/lazygit/releases/latest/download/lazygit_${LAZYGIT_VERSION}_Linux_x86_64.tar.gz"
-    tar xf /tmp/lazygit.tar.gz -C /tmp lazygit
-    sudo mv /tmp/lazygit /usr/local/bin/
-  fi
+if $IS_ARCH; then
+  $PKG_INSTALL lazygit
+else
+  LAZYGIT_VERSION=$(curl -ks "https://api.github.com/repos/jesseduffield/lazygit/releases/latest" | jq -r '.tag_name' | sed 's/v//')
+  curl -kLo /tmp/lazygit.tar.gz "https://github.com/jesseduffield/lazygit/releases/latest/download/lazygit_${LAZYGIT_VERSION}_Linux_x86_64.tar.gz"
+  tar xf /tmp/lazygit.tar.gz -C /tmp lazygit
+  sudo mv /tmp/lazygit /usr/local/bin/
 fi
-info "Lazygit installed"
+info "Lazygit installed/updated"
 
 mkdir -p ~/.config/lazygit
+backup_config ~/.config/lazygit/config.yml
 write_lazygit_config ~/.config/lazygit/config.yml
 info "Lazygit configured with $THEME_DISPLAY_NAME"