landing: v0.8.0 (s390x); playground on ndarray v0.8.0

[tannevaled]

Text only, no brand or CSS change.

• Version: library · v0.8.0 (simd(s390x): vector-facility kernels; native-endian AT_HWCAP ndarray#37).
• SIMD lists: s390x is added to the description and to the closing paragraph. The SIMD card is titled "SIMD on every 64-bit target" and now says the s390x kernels are validated under emulation only.
• playground/go.mod: ndarray v0.7.1 → v0.8.0, as localhost-f9 suggested, so its status line shows the current version. GOOS=js GOARCH=wasm go build passes.

🤖 Generated with Claude Code