Create QRCode for URL

### Describe the feature you'd like

First of all, thank you SO much for karakeep - I love it! :)

If you don't mind, I'd like to make a little (?) feature request:

It might be a nice feature if Karakeep were able to create a QRCode from a chosen URL directly.

That way it would be easy to share the URL with others (from mobile) easily, without copy/pasting the URL to a 3rd-party app.

I have no clue what it takes to implement this, so sorry if this is too much to ask.

### Describe the benefits this would bring to existing Karakeep users

Mobile users would be allowed to share their karakeep hoarded urls with others easily

### Can the goal of this request already be achieved via other means?

Alternatively you could use some custom QR code generator app and copy/paste a url from karakeep into the seperate app. I barely use mobile phones myself, so this might be no inconvenience for other users.

### Have you searched for an existing open/closed issue?

- [x] I have searched for existing issues and none cover my fundamental request

### Additional context

_No response_

The issue names no files, tests, or entry points. Start by locating the mobile flow for sharing a chosen saved URL and determine where a QR-code action would fit; done means users can generate and display a QR code for that URL without copying it to another app.

Written by the indexing model from the issue text.