License under GPLv3

Add SPDX headers to the source, a License section to the README, the
OFL notice for the bundled fonts, and ship LICENSE in the Docker image.

web/api.mjs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Copyright (C) 2026 Andy Dixon
 export function apiFetch(url, options = {}) {
   const headers = new Headers(options.headers);
   headers.set('ngrok-skip-browser-warning', 'true');