feat: allow setting 'base' via VITE_BASE_URL

this sets the default to `/` which results in this patch not breaking behavior. This is being used to set base as a relative path to enable hosting movie-web at any non-root location

vite.config.mts

@@ -24,6 +24,7 @@ const captioningPackages = [
 export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, process.cwd());
   return {
+    base: env.VITE_BASE_URL || '/',
     plugins: [
       million.vite({ auto: true, mute: true }),
       handlebars({