tpm-enrol: move signing key off the EK slot 0x81010001 → 0x81000100

Bench (Proxmox vTPM, host cygnus-cruiser-99) confirmed via tpm2_readpublic that
0x81010001 — the handle our design used for the fleet signing key — is the
TCG-standard RSA Endorsement Key slot: the object there is the swtpm-provisioned
EK (restricted|decrypt|adminwithpolicy, RSA-2048/AES128CFB, canonical EK
authPolicy 837197…, EK cert at NV 0x1c00002). Most firmware/swtpm TPMs occupy
that slot, so EnsureKey could never create our key there — it errored reading
the EK as ECC and enrolment died before the CSR/POST.

Move the fleet signing key to 0x81000100, a non-reserved owner persistent
handle (clear of EK 0x81010001/2 and SRK 0x81000001/2). Threaded through:
  - fleet-enrol -handle default + new rd.dot1x.handle= cmdline knob (baked by
    extract-artifacts.sh, overridable via SMBIOS)
  - files/etc/dot1x/wpa_supplicant-dot1x.conf private_key handle
  - the dracut hook, bench tpm-provision.sh / tpm-selftest.sh
  - CLAUDE.md invariant #1 + design/SSP docs + TODO #11
NV index 0x01800001 (owner range) is unchanged.

EnsureKey hardening: refuse to evict any restricted-decrypt object (EK/SRK) as
a safety net — never clobber the TPM endorsement/storage identity (also
protects the future EK/AK attestation path). Still self-heals a genuine stale
signing key. New regression TestEnsureKeyRefusesToEvictProtectedKey; the
stale-key regression and handle constants moved to 0x81000100.

Design note records the IDevID (0x81020001) option for the later EK/AK
attestation work. Follow-up items logged: content-aware NV presence check
(verify the cert chains to the fleet CA, so leftover/foreign NV can't suppress
enrolment) and a de-enrol/TPM-reset procedure.

serving/dot1x-bench/enrol/tpm-selftest.sh

@@ -4,7 +4,7 @@
 #
 # Run as root on a booted workstation (the open-port test image is fine — it
 # ships the same tooling). Uses SCRATCH handle/NV and cleans them up, so it never
-# touches the real 0x81010001 / 0x01800001. Pass --use-real-handles to exercise
+# touches the real 0x81000100 / 0x01800001. Pass --use-real-handles to exercise
 # the actual locations instead (still cleaned up unless --keep).
 #
 # It validates, in order:
@@ -24,7 +24,7 @@ for a in "$@"; do case "$a" in
 esac; done
 
 export TPM2TOOLS_TCTI="${TPM2TOOLS_TCTI:-device:/dev/tpmrm0}"
-if [ "$USE_REAL" = 1 ]; then HANDLE=0x81010001; NV=0x01800001
+if [ "$USE_REAL" = 1 ]; then HANDLE=0x81000100; NV=0x01800001
 else HANDLE=0x81008000; NV=0x01500000; fi
 
 WORK=$(mktemp -d); PASS=0; FAIL=0; SKIP=0