fix(qemu): use -cpu max so piCore64 binaries don't hit instruction aborts

piCore64's BusyBox segfaults under QEMU virt with -cpu cortex-a72, generating
an EL0 Instruction Abort (el0_ia in the panic call trace). The binary is built
with ARMv8 extensions (likely +lse atomics, +crypto, or +fp16) that the
cortex-a72 model doesn't enable by default.

Switch to -cpu max which enables all emulated ARMv8 features. This is fine for
dev testing; the actual production hosts (Graviton, Ampere, real ARM64
hardware) all have these features natively.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hack/dev-vm-arm64.sh

@@ -120,9 +120,13 @@ if [ "$MODE" = "disk" ]; then
     echo "    Press Ctrl+A X to exit QEMU"
     echo ""
 
+    # -cpu max enables all emulated ARMv8 features (atomics, crypto, fp16).
+    # piCore64's BusyBox is built with -march=armv8-a+crypto+lse and segfaults
+    # under -cpu cortex-a72 because some required extensions aren't on by
+    # default in that model.
     qemu-system-aarch64 \
         -machine virt \
-        -cpu cortex-a72 \
+        -cpu max \
         -m 2048 \
         -smp 2 \
         -nographic \
@@ -186,7 +190,7 @@ echo ""
 
 qemu-system-aarch64 \
     -machine virt \
-    -cpu cortex-a72 \
+    -cpu max \
     -m 2048 \
     -smp 2 \
     -nographic \