Set up MongoDB on this VM by following the exe.dev recipe at https://exe.dev/deploy/mongodb.md from top to bottom.

The recipe's example VM name is my-mongodb. This VM's name is the output of `hostname`: use it wherever the recipe writes my-mongodb. Skip the step that creates the VM; you are on it.

You are done when all of these are true. Check each one yourself:
- MongoDB 9.0 Community Edition, started at boot, listening on localhost only, with access control on.
- A one-member replica set, so transactions and change streams work.
- An `admin` user, and an `app` database with its own user and connection string in `~/mongodb/app.env`.
- Nightly backups with `mongodump`, one restored with `mongorestore` and checked.

Read the whole recipe, including the closed details. For initial setup,
follow "Install by hand" from top to bottom: the MongoDB repository and
server, the replica set and access control, log rotation, the app
database, the backup timer, and the scratch-server restore test. The
walkthrough sections are for the owner afterwards: don't import data,
set up Tailscale or Docker access, or run the Restore or Update
instructions during initial setup. Never overwrite an existing
~/mongodb/*.env file or /etc/mongod.keyfile. Leave the VM private and
do not reboot. Don't paste passwords into the chat; say they are in
~/mongodb/app.env and ~/mongodb/admin.env.

Finish with the URLs I should open and these commands, which only I can run, from my own computer (with this VM's name in them):
  ssh my-mongodb.exe.xyz cat mongodb/app.env
  ssh -N -L 27018:localhost:27017 my-mongodb.exe.xyz