feat: add QR code for room join

[ShubhamSPawade]

Adds a QR code modal to share the room URL for easier multi-device joining.

• Displays a QR code with the full room link (https://www.beatsync.gg/room/<roomId>)
• Adds a "Show QR Code" button on the room page
• Opens a modal with the QR code and a message below it
• Allows quick device joining by scanning the code

Benefits : Enables fast, error-free room joining across devices

[vercel]

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[ShubhamSPawade]

Hi! @freeman-jiang 👋, Just wanted to follow up on this PR. QR code joining is a small but powerful feature that really improves the multi-device experience. Would love to get your thoughts — I believe it's a must-have for seamless syncing. Thanks!

[MalTeeez]

@ShubhamSPawade looks awesome, could you maybe switch the url with one derived from the providers url, i.e. just from window.location.href to support multiple instances.

[ShubhamSPawade]

Hey! @MalTeeez My first PR should totally get merged in 😅 — it's a small addition but really improves multi-device syncing. I’ll update the QR code to use window.location.origin instead of the hardcoded URL so it supports self-hosted instances too. Will push that shortly!

[freeman-jiang]

Good effort, but needs a lot more polish before it's ready.

[ShubhamSPawade]

@freeman-jiang done with the changes.. please take a review

[ShubhamSPawade]

@freeman-jiang done with the changes.. please take a review

[freeman-jiang]

Please resolve conflicts and merge with main, would also be good if you can include an updated screenshot.