fix: guard success messages on command exit status

- Source x-path instead of capturing empty stdout via command substitution
- Validate --dry-run argument in cleanup script, reject unknown flags
- Gate success messages on preceding command's exit status with &&
- Applies to dfm (fmt, reset_nvim, shfmt) and install scripts
  (fonts, gh-extensions, python-packages, shellspec, z)

scripts/install-fonts.sh

@@ -51,8 +51,9 @@ install_fonts()
 {
   msgr run "Starting to install NerdFonts..."
   # shellcheck disable=SC2048,SC2086
-  ./install.sh -q -s ${fonts[*]}
-  msgr run_done "Done"
+  # shellcheck disable=SC2086
+  ./install.sh -q -s ${fonts[*]} \
+    && msgr run_done "Done"
   return 0
 }