Playability flags and card model cleanup

Added

• The server sends per-card playability and the active colour, which drives wild card display.

Changed

• The card model renames color to type across the contract, backend, and frontend.
• The build reads its version from the VERSION file.

Fixed

• Playable cards and the UNO prompt follow the server’s playability flag.
• The +4 stack penalty waits until the colour choice resolves.