Merge remote-tracking branch 'upstream/master'

feat(release): add riscv64 native build on self-hosted runner (#2)

• feat(release): add riscv64 native build on self-hosted runner

Replace the full upstream release workflow (macOS, Windows, CUDA, ROCm,
SYCL, openEuler, etc.) with a single riscv64 native build job on a
self-hosted BananaPi F3 runner. This fork only needs riscv64 binaries.

Key changes:

• Use GGML_NATIVE=ON instead of GGML_CPU_ALL_VARIANTS=ON to auto-detect
  zvfh (float16 vector) from /proc/cpuinfo on the SpacemiT K1
• Set CMAKE_BUILD_TYPE=Release for the single-config Makefile generator
• Self-hosted runner labels: [self-hosted, linux, riscv64]
• Release body uses github.repository for correct fork download URLs

• fix(release): clarify riscv64 binary is SpacemiT K1 native build

Add ISA extensions (rv64gcv_zvfh) to the download link and a note
that the binary is built with GGML_NATIVE=ON, so it may not run on
other riscv64 CPUs without the zvfh extension.

• feat(release): add generic riscv64 build for portable binary

Add a second build job (ubuntu-riscv64-generic) that compiles with
GGML_NATIVE=OFF, producing a scalar-only rv64gc binary that runs on
any riscv64 CPU. The native build (SpacemiT K1 optimized) is kept
as a separate asset for users with compatible hardware.