DOCFIX-187: opnsense-edge module boot fixes + boot-triple-fault incident report ...

Office1 OPNsense edge first-boot debugging. Several correct module fixes made;
the boot is NOT yet resolved (BTX-loader triple-fault under double-nested virt),
documented as an OPEN incident for the next session.

Module (opentofu/modules/opnsense-edge/main.tf), all kept (a working config
needs them, none resolved the fault):
- serial console (nano is serial-only; the module had none) + boot-log capture
- machine q35 -> i440fx (pc)
- disk COW-overlay -> direct per-VM copy (matches virt-install --import)
- CPU host-passthrough with AMD svm disabled (documented AMD nested-virt fix;
  note the provider key is `features` plural, not `feature`)

Incident report docs/incident-20260712-opnsense-edge-boot-triplefault.md: full
symptom (boot2 echoes /boot.config then triple-faults loading /boot/loader, a
consistent 262-byte fault confirmed fresh each boot), environment (double-nested
AMD Opteron_G3), everything tried, and ranked next steps (full CPU flags
+kvm_pv_eoi/+kvm_pv_unhalt, add a video device for the -D dual console, mem 4G,
UEFI/OVMF, outer-hypervisor CPU). Ledger checkpoint added; session at context
limit.

repo-lint 0 fail; module tofu validate Success.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>