v0.8.1

Fix: installer preflight crash on Debian & Fedora

• Preflight no longer aborts with $4: unbound variable. Adding the
  Fedora/Arch support in v0.8.0 grew the _pre_need_cmd helper to read $4/$5,
  but the Debian (3-arg) and Fedora (4-arg) call sites still passed fewer — so
  under the installer's set -euo pipefail the unbound argument killed the run
  before anything was installed.
• Fix: the optional hint args now default to empty (${4:-} / ${5:-}), so
  preflight survives on every OS. macOS and Arch were never affected.
• Thanks to the discussion bug report that pinpointed the exact line. 🙏

3. Final discussion answer

Fix: installer preflight crash on Debian & Fedora

• Preflight no longer aborts with $4: unbound variable. Adding the
  Fedora/Arch support in v0.8.0 grew the _pre_need_cmd helper to read $4/$5,
  but the Debian (3-arg) and Fedora (4-arg) call sites still passed fewer — so
  under the installer's set -euo pipefail the unbound argument killed the run
  before anything was installed.
• Fix: the optional hint args now default to empty (${4:-} / ${5:-}), so
  preflight survives on every OS. macOS and Arch were never affected.
• Thanks to @emad1234-msoudi and @makcodeir who pinpointed the exact line. 🙏