Illegal instruction on Raspberry Pi 4 (ARMv8)

## Environment
- Device: Raspberry Pi 4 (2GB) - Raspberry Pi 4 Model B Rev 1.2
- OS: Raspberry Pi OS Lite (64-bit)
- Architecture: ARMv8 (aarch64)
- Cactus version: latest main

## Steps to reproduce
1. cactus build --python
2. cactus run Qwen/Qwen3-0.6B --precision INT4
3. cactus run Qwen/Qwen3.5-0.8B --precision INT4

## Result
Illegal instruction

## Expected
Model runs as on Raspberry Pi 5

## Notes
Raspberry Pi 5 is ARMv8.2, Raspberry Pi 4 is ARMv8.0.
Likely compiled with instructions not supported on ARMv8.0.
Benchmarks on your README only show RPi 5 — is RPi 4 officially supported?

Reproduce the failure on a Raspberry Pi 4 using `cactus build --python` and the two `cactus run` commands with INT4 precision. Compare the build and runtime assumptions for ARMv8.0 against Raspberry Pi 5; done means the listed models run without an illegal instruction or the supported-device limitation is clearly documented.

Written by the indexing model from the issue text.