feat(setup): USB printer discovery — pick a real /dev/usb device

The kernel numbers usblp nodes by plug/boot order (park-buzi's printer
is lp1); the wizard hardcoded lp0 in labels/default and the admin had to
shell in and `ls /dev/usb`. Now:

- GET /api/setup/usb-printers enumerates /dev/usb/lpN (visible via the
  compose bind-mount) and enriches each with the printer's self-reported
  make/model from sysfs ieee1284_id (readable through Docker's ro /sys).
- The wizard's devicePath becomes a SELECT of printers actually present
  ("/dev/usb/lp1 — Xprinter XP-K200L"): a fresh form preselects the
  first real device; a saved-but-unplugged path stays selectable,
  flagged "saved — not present now"; zero found falls back to free text
  + a check-the-cable hint.
- Transport option label no longer hardcodes lp0.

Wiki: printer-usb-transport marked HARDWARE-VERIFIED (lab 2026-07-07:
full slip + feed + cut over USB — parity with TCP).

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

apps/web/src/SetupWizard.tsx

@@ -29,6 +29,7 @@ import {
   type RelayEvent,
   type RelaySpec,
   type TestResult,
+  fetchUsbPrinters,
 } from "./api.js";
 import { Modal } from "./ui/Modal.js";
 
@@ -546,6 +547,28 @@ function DeviceForm({
     }
     return out;
   });
+  // USB printers PRESENT on the box (/dev/usb/lpN + sysfs model) — fetched when a
+  // printer form is on the USB transport, so devicePath becomes a SELECT of real
+  // devices instead of a guessed path (the kernel may pick lp1 — park-buzi did).
+  const [usbPrinters, setUsbPrinters] = useState<{ path: string; description: string | null }[] | null>(null);
+  const usbTransport = isPrinter && String(config.transport ?? "tcp-ip") === "usb";
+  useEffect(() => {
+    if (!usbTransport) return;
+    let alive = true;
+    fetchUsbPrinters()
+      .then((r) => {
+        if (!alive) return;
+        setUsbPrinters(r.printers);
+        // Fresh form with no explicit path yet → preselect the first REAL device.
+        if (r.printers.length > 0) {
+          setConfig((c) => (c.devicePath == null ? { ...c, devicePath: r.printers[0]!.path } : c));
+        }
+      })
+      .catch(() => alive && setUsbPrinters([]));
+    return () => {
+      alive = false;
+    };
+  }, [usbTransport]);
   // Controllers: the unified relay map. Each relay reacts to an EVENT — entry/exit/both
   // (pulse a barrier) or radarAlert (drive an alert lamp). Alert relays carry a trigger
   // input + blink cadence; barriers carry no input wiring (that lives in `inputs` below).
@@ -890,7 +913,32 @@ function DeviceForm({
                 {f.label}
                 {f.required ? " *" : ""}
               </label>
-              {f.type === "select" ? (
+              {f.key === "devicePath" && usbPrinters != null && usbPrinters.length > 0 ? (
+                // Real devices found → a select (path + self-reported model). A saved
+                // path that is NOT currently present stays selectable, flagged.
+                <select
+                  className="select"
+                  value={String(config.devicePath ?? (f.default as string | undefined) ?? "")}
+                  onChange={(e) => {
+                    const v = e.target.value;
+                    setConfig((c) => ({ ...c, devicePath: v }));
+                    resetStatus();
+                  }}
+                >
+                  {(() => {
+                    const cur = String(config.devicePath ?? (f.default as string | undefined) ?? "");
+                    const missing = cur && !usbPrinters.some((u) => u.path === cur);
+                    return [
+                      ...(missing ? [{ path: cur, description: t("setup.usbSavedMissing") }] : []),
+                      ...usbPrinters,
+                    ].map((u) => (
+                      <option key={u.path} value={u.path}>
+                        {u.description ? `${u.path} — ${u.description}` : u.path}
+                      </option>
+                    ));
+                  })()}
+                </select>
+              ) : f.type === "select" ? (
                 <select
                   className="select"
                   value={String(config[f.key] ?? (f.default as string | number | undefined) ?? "")}
@@ -945,6 +993,9 @@ function DeviceForm({
                   }}
                 />
               )}
+              {f.key === "devicePath" && usbPrinters != null && usbPrinters.length === 0 && (
+                <p className="hint mt-1">{t("setup.usbNoneFound")}</p>
+              )}
             </div>
             ),
           )}