Add bootstrap.sh with zsh and git modules

Cross-distro (RHEL/Debian) VM setup: zsh + oh-my-zsh with a self-healing
bash fallback for environments that reset the root filesystem or hardcode
bash for new terminals (e.g. Kasm Workspaces), plus git identity and
HTTPS credential-store configuration.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bootstrap.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env sh
+# bootstrap.sh — entrypoint for configuring a fresh VM (RHEL-family or
+# Debian-family) with this repo's dotfiles. Safe to re-run.
+#
+#   curl -fsSL https://git.nic-oconnor.com/public/dotfiles/raw/branch/main/bootstrap.sh | sh
+#   (or, from a checked-out clone: ./bootstrap.sh)
+set -eu
+
+SCRIPT_DIR="$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)"
+
+"$SCRIPT_DIR/zsh/install.sh"
+"$SCRIPT_DIR/git/install.sh"