docs(wiki): ATECC608 is upcoming — retag ledger signing to the on-host reality

No secure element is on-site: event signing runs on the software HMAC
(EVENT_SIGNING_KEY, an env var on the host disk), so the ledger is
tamper-EVIDENT but forgeable by anyone who owns the host. Several pages
overstated it as present-tense "ATECC608-signed / unforgeable"; correct them.

- NEW concepts/hardware-signer-options.md: four options for a non-extractable
  signing key (USB HSM / YubiKey / reuse the TPM / plain-dongle trap) + the
  recommendation (TPM interim → USB-HSM target; ATECC608 stays for the embedded
  ESP32, wrong part for a PC host).
- entities/atecc608.md: UPCOMING-not-present status banner + PC-vs-embedded.
- disk-os-hardening.md: fix the live-USB row (BIOS boot-order password is
  load-bearing, not Secure Boot — a signed live USB runs); add a physical-tamper
  chain (Dell 7070 CMOS-reset → live-USB → PCR-7 same-signer unseal) + accepted
  risks (that unseal, unsigned-initramfs evil-maid, operator-USB read TODO).
- open-questions #6 reframed; standing-decisions / overview / threat-model /
  index de-overstated; log query entry.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

wiki/overview.md

@@ -25,9 +25,11 @@ deployed on-site at a parking facility. Two forces shape nearly every decision:
   [[react-vite-spa]] · [[sqlite]] + [[drizzle-orm]] · [[local-jwt-auth]] — all open-licensed to
   avoid lock-in (cf. rejected [[payload-cms]], [[refine]], [[logto-zitadel-oidc]]). The operator UI
   ships as a thin **[[desktop-shell-tauri|Tauri v2]]** kiosk shell (chosen over Electron).
-- **Integrity** is the heart of it: an [[append-only-event-chain]] (hash-chained, [[atecc608]]-
-  signed) plus external [[reconciliation]] — *that's* what remote sync really is. Encryption at
-  rest ([[disk-os-hardening]]) defends a secondary threat.
+- **Integrity** is the heart of it: an [[append-only-event-chain]] (hash-chained, signed) plus
+  external [[reconciliation]] — *that's* what remote sync really is. Signing is **software today**
+  (key on-disk → forgeable by a host owner); a non-extractable **hardware signer** (TPM / USB-HSM;
+  the [[atecc608]] is upcoming) is the pending fix — [[hardware-signer-options]]. Encryption at rest
+  ([[disk-os-hardening]]) defends a secondary threat.
 - **Devices** sit behind a [[device-adapter-pattern]] (swap hardware → new adapter only), with
   the [[barrier-not-a-door]] safety principle keeping physical safety in barrier-operator firmware.
 - **Access control** today is the **[[dingtian-relay]]** relay+input controller behind