docs(wiki): printer USB transport + open-question for the provisioning

New concepts/printer-usb-transport.md (the seam, usblp char device,
reachability-only status, threat model). open-questions #14: confirm the
on-site printer is USB and bake the usblp + udev write-access rule into the
appliance image (provisioning, not app code; unverified on hardware). Updated
rongta-printer.md (USB transport note), index.md, log.md.

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

wiki/entities/rongta-printer.md

@@ -34,6 +34,13 @@ many ESC/POS-compatible OEM clones that share its firmware). Driver `rongta` in
   We scrape that rather than hand-decode `DLE EOT` — this clone's DLE EOT reply bytes do **not**
   match the canonical ESC/POS bit layout (verified on hardware), so trusting the device's own
   decode avoids a false-healthy. Implemented as `readStatus()`; see [[printer-status-monitoring]].
+- **USB transport (added 2026-06-24).** The same driver can instead drive a printer over a local
+  USB `usblp` char device (`/dev/usb/lp0`) — `config.transport` (`tcp-ip` | `usb`) picks the wire
+  behind one render layer (the ESC/POS bytes are identical). The status web page is a **network**
+  feature, so a **USB Rongta degrades to reachability-only** monitoring (open-the-node probe, no
+  paper/cover verdict — the same honesty floor as the Cashino). Driving USB depends on the appliance
+  image (`usblp` bound + a udev write-access rule) — a provisioning step, open-questions #14. Full
+  rationale in [[printer-usb-transport]].
 
 ## Deployment (this site)