Add webcam QR code scanning support when commissioning Matter devices via the web UI

[mzspicoli]

Describe the enhancement

The problem

When adding a Matter device through the Home Assistant web interface (Settings → Matter → Add device → Add manually), the only option available is to manually type the commission code in a text input field. There is no way to scan the QR code using the computer's webcam.

Proposed solution

Add a "Scan QR code" button to the Matter "Add device" dialog in the web frontend that activates the user's webcam to scan the Matter QR code directly from the browser — similar to how the Z-Wave integration already implements QR code scanning for SmartStart device provisioning.

Device or feature details

This is not specific to a single device, it applies to all Matter devices that use QR codes for commissioning.

Use cases

As a user who manages Home Assistant primarily from a desktop browser, I frequently add new Matter devices. With webcam QR scanning in the web UI, I could simply hold the device's QR code up to my laptop's webcam and have the commission code auto-filled instantly

Anything else?

No response