Lifts v0.4.0's implicit x86_64-only assumption and stops pulling
linux-only display server crates into Windows/macOS builds.

- simd_queue.rs: AVX2 + BMI1 path gated behind
  cfg(target_arch = "x86_64"); scalar fallback compiled on every other
  target (signature parity preserved).
- Cargo.toml: eframe wayland/x11 features moved into a
  [target.'cfg(target_os = "linux")'.dependencies] block.

Apple Silicon / aarch64 / non-x86_64 builds now compile. Host build,
clippy, fmt, tests all still green on x86_64-linux.