Add rgb-card-background-color to fix QR codes

[Nezz]

Add rgb-card-background-color to fix QR codes. It seems that this variable was meant to be the same as the card background color, but without the alpha component. I'm not sure why this variable is used to generate QR codes instead of hardcoded #000 and #fff, but I guess the idea behind doing that in home-assistant/frontend#19726 was dark mode support.

Resolves #60 and the issue mentioned in #64 (comment)

Note: I regenerated the themes in commit a869137. Maybe it's due to using a different OS, but this line

for background in Path("themes").glob("homekit-bg-*.jpg"):

returns the images in alphabetical order for me, whereas they were in a seemingly random order previously.

Commit 19f550b contains the clean diff of the theme files.

[Nezz]

The QR code now works and can be scanned by the Tuya app with a dark mode theme. No screenshot proof this time to avoid doxxing myself.

[basnijholt]

Great! Could you perhaps change:

Path("themes").glob("homekit-bg-*.jpg")

to sorted(Path("themes").glob("homekit-bg-*.jpg")) to make it deterministic?

[Nezz]

Sure, changed. There were no changes to the theme files.

[basnijholt]

Awesome! Thanks again 😄