Please add SOME authentication

- [x] I am on the [latest](https://github.com/ActivityWatch/activitywatch/releases/latest) ActivityWatch version.
- [x] I have searched the issues of this repo and believe that this is not a duplicate.

- **OS name and version**: Ubuntu 24.04
- **ActivityWatch version**: v0.13.2

## Describe the bug

Currently aw_server allows any process that can access 127.0.0.1:5600 full access.

This makes the whole security hinge on the impossibility to access 127.0.0.1:5600

## To Reproduce

Anything with the functionality of curl can download all data, example
with default setup:
```
watchers=`curl -s 'http://127.0.0.1:5600/api/0/buckets/' | grep 'aw-watcher[^"]*' -o`
for w in $watchers ; do curl -s "http://127.0.0.1:5600/api/0/buckets/$w/export" >> export ; done
```

## Expected behavior

I expect that curl needs a security cookie or password to access the data

## Additional context

There is some discussion already here https://github.com/ActivityWatch/activitywatch/issues/32, but it seems to miss the point that this is a problem with the 1 user localhost only setup already
The idea of "Defense in depth" is that you add authentication because its trivial and makes the setup much more secure. Without any authentication a single bug in the browser or in java script, or in the firewall or in ANY application running on the same machiene could allow an attacker to access everything