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.

files/etc/dot1x/wpa_supplicant-dot1x.conf

@@ -14,8 +14,11 @@ network={
     client_cert="/run/dot1x/client.pem"
 
     # BENCH-VERIFY: TPM key reference method on your wpa_supplicant build.
+    # Handle is the fleet signing-key handle (non-reserved owner handle; NOT the
+    # EK slot 0x81010001 — see CLAUDE.md invariant #1). Keep in sync with the
+    # enrolment -handle / rd.dot1x.handle default.
     # Option A (OpenSSL tpm2 provider, direct persistent handle):
-    private_key="handle:0x81010001"
+    private_key="handle:0x81000100"
     # Option B (tpm2-pkcs11 with a store regenerated into /run at boot):
     # private_key="pkcs11:token=fleet;object=dot1x-key;type=private;pin-value=..."