Make scripts/dev-setup.sh POSIX-portable

The contributor bootstrap script was bash-only ('#!/usr/bin/env bash',
'set -euo pipefail', '[[ ... == ... ]]') while install.sh and
uninstall.sh are POSIX sh. Consistency lines them up:

  - shebang -> '#!/usr/bin/env sh'
  - 'set -euo pipefail' -> 'set -eu' (pipefail isn't POSIX; not needed
    here either, no risky pipelines in this script)
  - '[[ ... == ... ]]' -> '[ ... = ... ]'

Also added a 'bun run test' hint to the post-install workflow note now
that there's a test suite to run.

scripts/dev-setup.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 #
 # dev-setup.sh - contributor bootstrap for the `move` repo.
 #
@@ -11,13 +11,17 @@
 #
 # This script is idempotent: re-running it just re-resolves the dependency
 # tree against the existing `bun.lock`.
+#
+# POSIX sh; no bashisms. Matches the style of install.sh / uninstall.sh.
 
-# Fail fast on any error, unset variable, or failed pipe stage.
-set -euo pipefail
+# Fail fast on any error or unset variable. (`pipefail` is bash-only and
+# not strictly needed here; this script doesn't pipe in failure-prone
+# ways.)
+set -eu
 
-# Operate at the repo root regardless of the caller's CWD. This script lives
-# under scripts/, so pop up one level to land at the project root before
-# running bun install.
+# Operate at the repo root regardless of the caller's CWD. This script
+# lives under scripts/, so pop up one level to land at the project root
+# before running bun install.
 cd "$(dirname "$0")/.."
 
 echo "==> Checking for Bun..."
@@ -36,13 +40,14 @@ bun install
 echo
 echo "Done. Dev workflow:"
 echo "  - 'bun run start' to run from the source tree."
+echo "  - 'bun run test' to run the test suite."
 echo "  - 'bun link' to install a global 'move' command pointed at this checkout."
 echo "End-user installer is install.sh (curl-pipeable from Gitea)."
 
 # macOS gates synthetic mouse events behind the Accessibility permission.
 # Without this hint, the first run silently fails to move the cursor and
 # the user has no obvious next step.
-if [[ "$(uname)" == "Darwin" ]]; then
+if [ "$(uname)" = "Darwin" ]; then
     echo "Note: macOS will prompt for Accessibility permission on first mouse move."
     echo "      Grant it under System Settings > Privacy & Security > Accessibility."
 fi