Make script/ entrypoints POSIX sh; add bootstrap and setup

script/install-precommit

@@ -1,15 +1,15 @@
-#!/usr/bin/env bash
+#!/bin/sh
 # script/install-precommit: install the git pre-commit hook that runs
 # script/precommit. Our own extension to scripts-to-rule-them-all.
-set -euo pipefail
+set -eu
 
-ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd -P)"
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    local hook=".git/hooks/pre-commit"
-    printf '#!/bin/sh\nset -e\nscript/precommit\n' > "$hook"
-    chmod +x "$hook"
+    hook=".git/hooks/pre-commit"
+    printf '#!/bin/sh\nset -e\nscript/precommit\n' > .git/hooks/pre-commit
+    chmod +x .git/hooks/pre-commit
     echo "pre-commit hook installed: runs script/precommit"
 }