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.

CLAUDE.md

@@ -103,10 +103,13 @@ instead of working around it.
 
 1. **No per-host state in any artifact, ever.** No hostnames, keys, certs,
    MACs, or per-host config in the initramfs, rootfs, UKI, or OCI image.
-   All host identity derives from the TPM at runtime (key at persistent
-   handle `0x81010001`, cert at NV index `0x01800001`, hostnqn derived from
-   the cert serial). If a change needs per-host data, it belongs in the
-   enrolment flow, not the image.
+   All host identity derives from the TPM at runtime (signing key at persistent
+   handle `0x81000100` — a **non-reserved owner handle**, deliberately NOT the
+   EK slot `0x81010001` nor the SRK `0x81000001`, which firmware/swtpm
+   provisioning already occupy; cert at NV index `0x01800001`, hostnqn derived
+   from the cert serial). If a change needs per-host data, it belongs in the
+   enrolment flow, not the image. (The handle is overridable via
+   `rd.dot1x.handle=` / `fleet-enrol -handle`.)
 1. **The hook ordering in `dot1x-macsec-up.sh` is load-bearing.**
    NV-cert extraction → supplicant start → wait for `Authorized` + macsec0 →
    DHCP **on macsec0** → hostnqn derivation. Never DHCP before auth