Add QR Codes, Links, and tracking

[jgoldberger26]

This PR adds a link resolver under the /r/ api. The link resolver tracks users that pass through it, and can generate QR Codes to those links for easy sharing.

Would address https://linear.app/capyrpi/issue/CAPS-29/qr-code-generation-and-tracking

TODO still:

• Stylize QR Codes
• Check additional steps that need to be done for migrating to postgres18.

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[jgoldberger26]

I won't have time today to decouple users from links (the current implementation will allow unregistered users to have a null uid, otherwise it will be tracked), so I resolved merge conflicts and am opening this PR. @YaoxuanZhang if you want to use it for your edit Wednesday, feel free to approve and pull these changes into main. Otherwise I will add device tracking next week after we resubmit sprint 1.

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