blink: redirect on root route (#8029)

* make root route redirect to 301

* use config

* end

* add a comment

bskylink/src/routes/root.ts

@@ -0,0 +1,14 @@
+import {Express} from 'express'
+
+import {AppContext} from '../context.js'
+import {handler} from './util.js'
+
+export default function (ctx: AppContext, app: Express) {
+  return app.get(
+    '/',
+    handler(async (_req, res) => {
+      res.setHeader('Location', `https://${ctx.cfg.service.appHostname}`)
+      return res.status(301).end()
+    }),
+  )
+}