fix(access): ban guest-agent as access channel — SSH only [#403]

Previous sessions used `qm guest exec` to back-door SSH keys into ~30 VMs,
bypassing sshd's audit trail in an ITAR/CMMC environment. Wire the ban deep
so it cannot recur:

- tests/remote.sh: remove the vm-guest mode + qm-guest-exec path entirely
- scripts/check-rules.sh: rule #11 fails on any `qm guest exec` / `vm-guest`
  pattern in code (scans .sh/.bash/.py; docs may describe the ban freely)
- AGENTS.md: codify "Access-channel policy: SSH only" as non-negotiable;
  add "Questions" rule banning harness question tools (use questions-v1.md)
- tests/vm-validation.sh: drop guest-agent key re-injection; SSH-only
- proxmox/perf/scripts/perf-matrix.sh + deploy-tuned-guests.sh: convert
  guest-agent execution to SSH (vmroot) now that VMs have key + sudo
- bootstrap-all.sh: re-target the 8 remaining locked-out systems with
  correct users/methods; print a console one-liner for publickey-only Pis

Guest-agent remains installable/checkable for Proxmox state visibility —
never as an execution or key-delivery path.

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

tests/remote.sh

@@ -30,8 +30,6 @@ PROX_HOST="${PROX_HOST:-pfv-tsys5}"
 PROX_USER="${PROX_USER:-root}"
 VM_IP="${VM_IP:-192.168.3.50}"
 VM_USER="${VM_USER:-localuser}"
-VM_ID="${VM_ID:-}"
-GUEST_TIMEOUT="${GUEST_TIMEOUT:-900}"
 
 SSH_OPTS=(-o BatchMode=yes -o StrictHostKeyChecking=accept-new -o ConnectTimeout=15)
 
@@ -55,33 +53,6 @@ _copy() {
   fi
 }
 
-# Out-of-band VM access via the Proxmox qemu-guest-agent. This runs commands
-# as root inside the VM and does NOT depend on SSH, so it works even after
-# secharden-ssh replaces authorized_keys and secharden-2fa enforces
-# publickey+keyboard-interactive (which blocks non-interactive SSH).
-GUEST_PARSER="/root/.knel-guest-parse.py"
-GUEST_PARSER_SRC="import sys, json
-try:
-    d = json.load(sys.stdin)
-except Exception:
-    sys.exit(3)
-sys.stdout.write(d.get('out-data', '') or '')
-sys.stderr.write(d.get('err-data', '') or '')
-ec = d.get('exitcode', 1)
-sys.exit(ec if ec is not None else 1)"
-
-_ensure_guest_parser() {
-  if _prox "test -f '$GUEST_PARSER'" >/dev/null 2>&1; then return 0; fi
-  printf '%s\n' "$GUEST_PARSER_SRC" | _prox "cat > '$GUEST_PARSER'" >/dev/null 2>&1
-}
-
-_vm_guest() {
-  [ -n "$VM_ID" ] || die "vm-guest requires VM_ID"
-  _ensure_guest_parser
-  local cmdb64; cmdb64="$(printf '%s' "$*" | base64 -w0)"
-  _prox "qm guest exec $VM_ID --timeout ${GUEST_TIMEOUT} -- /bin/sh -c 'echo $cmdb64 | base64 -d | /bin/sh' 2>/dev/null | python3 '$GUEST_PARSER'"
-}
-
 mode="${1:-}"; shift || true
 case "$mode" in
   prox)         [ "$#" -ge 0 ] || die "need command"; _prox "$*" ;;
@@ -91,7 +62,6 @@ case "$mode" in
   vm-file)      [ -f "${1:-}" ] || die "need local script file"; _vm "bash -s" < "$1" ;;
   vm-copy)      [ -f "${1:-}" ] || die "need local file"; _copy "${VM_USER}@${VM_IP}" "$1" "${2:-}" ;;
   prox-copy)    [ -f "${1:-}" ] || die "need local file"; _copy "${PROX_USER}@${PROX_HOST}" "$1" "${2:-}" ;;
-  vm-guest)     [ "$#" -ge 1 ] || die "need command"; _vm_guest "$*" ;;
   ""|-h|--help|help) sed -n '2,40p' "${BASH_SOURCE[0]}" >&2; exit 0 ;;
   *) die "unknown mode '$mode'. Run '$0 help'." ;;
 esac