go.mod: bump go-microvm to v0.0.32

[JAORMX]

Summary

Picks up the security hardening series released in
go-microvm v0.0.32.

Included upstream changes:

• Symlink-safe rootfs hooks (authorized_keys, file, env, VM
  config). Hooks refuse symlink components planted by a
  malicious OCI layer, closing a host-write vector on the
  InjectAuthorizedKeys / InjectFile / InjectEnvFile paths
  brood-box uses in every VM.
• OCI layer-apply whiteouts now validate each path component
  before RemoveAll / ReadDir. Tar-entry count capped at 1 M to
  bound inode exhaustion.
• DNS interceptor filters Answer A records by CNAME bailiwick
  and caps dynamic egress-rule TTL at 5 min.
• Firewall relay caps frame length at 65 KiB and drops non-IPv4
  non-ARP frames under deny-default.
• Hosted gateway services ship with default HTTP timeouts
  (Slowloris-proof).
• terminateStaleRunner refuses to signal a PID that does not
  belong to the expected runner binary.
• Any firewall configuration (rules, non-Allow default, or
  egress policy) now auto-wires the hosted provider.
• Extract cache dir is 0o700; each extraction records per-file
  SHA-256 and re-verifies on Ensure.

No brood-box code changes required — all hardening is wired
through interfaces brood-box already uses.

Test plan

• task build --force rebuilds bbox against v0.0.32 runtime
• task verify green (fmt + lint + full test suite)
• End-to-end: bbox claude-code --no-mcp --exec /bin/bash
  boots the VM, hooks run, workspace R/W round-trip
  flushes, DNS egress allows api.anthropic.com and
  denies unknown hosts

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