add setup.sh bootstrap script and openai to requirements

setup.sh creates a .venv, installs deps, and seeds .env from .env.example.
Idempotent on re-run. Adds openai alongside anthropic so s01-s05 (OpenAI)
and s06+ (still Anthropic) both work.

requirements.txt

@@ -1,3 +1,4 @@
+openai>=1.40.0
 anthropic>=0.25.0
 python-dotenv>=1.0.0
 pyyaml>=6.0

setup.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+# Dev environment bootstrap for learn-claude-code.
+# Creates a local .venv, installs requirements.txt, and seeds .env from
+# .env.example. Safe to re-run -- existing venv and .env are preserved.
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$REPO_ROOT"
+
+VENV_DIR="${VENV_DIR:-.venv}"
+PYTHON_BIN="${PYTHON_BIN:-python3}"
+MIN_PY_MAJOR=3
+MIN_PY_MINOR=10
+
+say() { printf '\033[36m==>\033[0m %s\n' "$*"; }
+warn() { printf '\033[33m[warn]\033[0m %s\n' "$*" >&2; }
+die()  { printf '\033[31m[error]\033[0m %s\n' "$*" >&2; exit 1; }
+
+# 1. Check Python
+if ! command -v "$PYTHON_BIN" >/dev/null 2>&1; then
+  die "'$PYTHON_BIN' not found. Install Python ${MIN_PY_MAJOR}.${MIN_PY_MINOR}+ or set PYTHON_BIN."
+fi
+
+PY_VERSION="$("$PYTHON_BIN" -c 'import sys; print("%d.%d" % sys.version_info[:2])')"
+say "Using $PYTHON_BIN ($PY_VERSION)"
+
+"$PYTHON_BIN" - <<PY || die "Python ${MIN_PY_MAJOR}.${MIN_PY_MINOR}+ required (found $PY_VERSION)."
+import sys
+sys.exit(0 if sys.version_info >= (${MIN_PY_MAJOR}, ${MIN_PY_MINOR}) else 1)
+PY
+
+# 2. Create venv
+if [ ! -d "$VENV_DIR" ]; then
+  say "Creating virtualenv at $VENV_DIR"
+  "$PYTHON_BIN" -m venv "$VENV_DIR"
+else
+  say "Reusing virtualenv at $VENV_DIR"
+fi
+
+# shellcheck disable=SC1091
+source "$VENV_DIR/bin/activate"
+
+# 3. Install deps
+say "Upgrading pip"
+python -m pip install --upgrade pip >/dev/null
+
+say "Installing requirements.txt"
+python -m pip install -r requirements.txt
+
+# 4. Seed .env
+if [ ! -f .env ]; then
+  if [ -f .env.example ]; then
+    say "Creating .env from .env.example"
+    cp .env.example .env
+    warn "Edit .env and set your API key + MODEL_ID before running the agents."
+  else
+    warn "No .env.example found; skipping .env creation."
+  fi
+else
+  say ".env already exists (leaving as-is)"
+fi
+
+# 5. Quick import sanity check
+say "Verifying imports"
+python - <<'PY'
+import importlib, sys
+missing = [m for m in ("openai", "dotenv", "yaml") if not importlib.util.find_spec(m)]
+if missing:
+    sys.exit(f"Missing modules after install: {missing}")
+print("  openai, python-dotenv, pyyaml OK")
+PY
+
+cat <<EOF
+
+Done. Activate the venv and try an agent:
+
+  source $VENV_DIR/bin/activate
+  # edit .env to set OPENAI_API_KEY, OPENAI_BASE_URL (optional), MODEL_ID
+  python agents/s01_agent_loop.py
+
+EOF