Add local Arti provider bootstrap

tools/browser-tor-provider-build.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+set -eu
+
+root="${AMPB_BROWSER_BUILD_ROOT:-/tmp/ampb-browser-build}"
+provider_root="$root/providers/arti"
+log="$root/logs/arti-cargo-install.log"
+
+mkdir -p "$root/logs"
+mkdir -p "$root/providers"
+
+cargo install arti --locked --root "$provider_root" >"$log" 2>&1
+
+binary="$provider_root/bin/arti"
+if [ ! -x "$binary" ]; then
+  printf 'missing arti binary after install: %s\n' "$binary" >&2
+  exit 1
+fi
+
+version="$("$binary" --version | head -n 1)"
+printf 'AMPB_TOR_PROVIDER status=ok kind=arti binary=%s log=%s version="%s"\n' "$binary" "$log" "$version"