feat(scripts): add shellspec installation to dfm

Add install-shellspec.sh script that clones shellspec to
~/.cache/shellspec and installs via make to ~/.local/bin.
Wire it into dfm install menu and the Tier 4 install-all pipeline.

local/bin/dfm

@@ -88,6 +88,7 @@ section_install()
     "nvm-latest:Install latest lts node using nvm"
     "nvm:Install Node Version Manager (nvm)"
     "python-packages:Install Python packages via uv"
+    "shellspec:Install shellspec testing framework"
     "xcode-cli-tools:Install Xcode CLI tools (macOS)"
     "z:Install z"
   )
@@ -121,6 +122,7 @@ section_install()
       $0 install ntfy
 
       # Tier 4: Independent utilities
+      $0 install shellspec
       $0 install z
 
       msgr msg "Reloading configurations again..."
@@ -245,6 +247,12 @@ section_install()
         && msgr yay "Xcode CLI tools installed!"
       ;;
 
+    shellspec)
+      msgr run "Installing shellspec..."
+      bash "$DOTFILES/scripts/install-shellspec.sh" \
+        && msgr yay "shellspec has been installed!"
+      ;;
+
     z)
       msgr run "Installing z..."
       bash "$DOTFILES/scripts/install-z.sh" \

scripts/install-shellspec.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -euo pipefail
+# @description Install shellspec testing framework
+#
+# shellcheck source=shared.sh
+source "${DOTFILES}/config/shared.sh"
+
+SHELLSPEC_REPO="https://github.com/shellspec/shellspec.git"
+SHELLSPEC_CACHE="$HOME/.cache/shellspec"
+
+install_shellspec()
+{
+  if [[ -d "$SHELLSPEC_CACHE" ]]; then
+    msgr ok "shellspec repo already cloned, pulling latest..."
+    git -C "$SHELLSPEC_CACHE" pull --quiet
+  else
+    git clone --depth 1 "$SHELLSPEC_REPO" "$SHELLSPEC_CACHE"
+  fi
+
+  msgr run "Running make install..."
+  make -C "$SHELLSPEC_CACHE" install PREFIX="$HOME/.local"
+  msgr run_done "shellspec installed to $HOME/.local/bin/shellspec"
+  return 0
+}
+
+main()
+{
+  install_shellspec
+  return 0
+}
+
+main "$@"