Support RISC-V (rv64)

[jserv]

kbox is considered riscv64-supported when:

• Builds successfully with make ARCH=riscv64
• Runs on QEMU (qemu-system-riscv64) without patches
• Works with a standard rootfs (Alpine Linux)

[jserv]

RISE RISC-V Runners is a managed GitHub Actions runner service that executes CI/CD workflows on real RISC-V hardware. Install the GitHub App on your organization or personal account, set runs-on: ubuntu-24.04-riscv in workflow, and jobs will run on dedicated RISC-V nodes with full Docker support. No emulation, no cross-compilation required.

RISE provides this service free of charge for open source projects. We can explore enabling this service for RISC-V target deployment and validation.

[jserv]

@rota1001 , Before reworking #19, could you submit CI/CD changes to utilize RISC-V Runners?