feat: add install.sh posix bootstrap

install.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+set -e
+REPO="https://raw.githubusercontent.com/Abdess/retrobios/main"
+SCRIPT=$(mktemp)
+trap 'rm -f "$SCRIPT"' EXIT
+if command -v curl >/dev/null 2>&1; then
+  curl -fsSL "$REPO/install.py" -o "$SCRIPT"
+elif command -v wget >/dev/null 2>&1; then
+  wget -qO "$SCRIPT" "$REPO/install.py"
+else
+  echo "Error: curl or wget required" >&2; exit 1
+fi
+PYTHON=""
+for cmd in python3 python; do
+  if command -v "$cmd" >/dev/null 2>&1; then PYTHON="$cmd"; break; fi
+done
+if [ -z "$PYTHON" ]; then
+  echo "Error: Python 3 required" >&2; exit 1
+fi
+"$PYTHON" "$SCRIPT" "$@"