feat(setup): print a real test slip from the printer "Test connection" modal

healthCheck only opens the transport (TCP connect / USB open) — it proves the
printer is REACHABLE, not that paper feeds and the head fires. Add a "Print test
slip" action so the admin can physically confirm a printer is live (the new
host-net USB /dev/usb/lpN path, or a network printer).

- server: POST /api/setup/test-print — printer-only, re-merges stored secrets like
  /test (so an edited network printer authenticates), creates the device, and pushes
  a short slip via the device-agnostic printReport(). Fail-soft: a print error
  (paper out, head fault, transport drop) is reported, never a 500. Mirrors the
  test-anpr pattern.
- web: testPrint() client + PrintTestResult; a button in the device modal shown for
  category=printer, with ok/fail rendering. i18n keys in sq + en (parity holds).

Server 168 tests pass; web + server typecheck clean.

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

apps/server/src/routes/setup.ts

@@ -7,6 +7,7 @@ import {
   isCamera,
   isDiscoverable,
   isHardenable,
+  isPrinter,
   registerBuiltinDrivers,
   registry,
   setDeviceLogSink,
@@ -391,6 +392,70 @@ export async function setupRoutes(
     },
   );
 
+  // Print a TEST SLIP on a printer config WITHOUT saving. healthCheck only opens the
+  // transport (TCP connect / USB open) — it proves reachability, NOT that paper feeds
+  // and the head fires. This pushes a real short slip through the device-agnostic
+  // printReport(), so the admin can physically confirm the printer is live (the USB
+  // /dev/usb/lpN path or the network printer). Fail-soft like test-anpr: a print error
+  // is reported, never a 500. Mirrors /test's stored-secret re-merge so an edited
+  // network printer still authenticates.
+  app.post<{ Body: TestBody }>(
+    "/api/setup/test-print",
+    { preHandler: adminGuard },
+    async (req, reply) => {
+      const { driverId, config, id } = req.body;
+      const driver = registry.get(driverId);
+      if (!driver) return reply.code(400).send({ error: `unknown driver: ${driverId}` });
+      if (driver.category !== "printer") {
+        return reply.code(400).send({ error: `driver ${driverId} is not a printer` });
+      }
+
+      const merged: Record<string, string | number | boolean | undefined> = { ...config };
+      if (id) {
+        for (const [k, v] of Object.entries(storedSecrets(db, id, driverId, config))) {
+          const sent = merged[k];
+          if (sent === undefined || sent === "" || sent === 0) merged[k] = v as string | number;
+        }
+      }
+
+      let device;
+      try {
+        device = registry.create(driverId, merged as Record<string, string | number | boolean>);
+      } catch (err) {
+        return reply.code(400).send({ error: (err as Error).message });
+      }
+      if (!isPrinter(device)) {
+        return reply.code(400).send({ error: `driver ${driverId} cannot print` });
+      }
+
+      const startedAt = Date.now();
+      try {
+        await device.printReport({
+          title: "TEST PRINT",
+          lines: [
+            "Parking System",
+            "Printer test slip",
+            new Date().toLocaleString("sv"), // YYYY-MM-DD HH:MM:SS, locale-stable
+            "",
+            "If you can read this, the",
+            "printer is connected and",
+            "printing correctly.",
+          ],
+        });
+      } catch (err) {
+        // The failure we're testing for (paper out, head fault, transport drop) —
+        // report it, don't 500.
+        return reply.send({
+          ok: false,
+          reason: "print-failed",
+          detail: (err as Error).message,
+          tookMs: Date.now() - startedAt,
+        });
+      }
+      return reply.send({ ok: true, tookMs: Date.now() - startedAt });
+    },
+  );
+
   // Candidate backend IPs the device can push to, for a given device host. The
   // wizard pre-fills with the on-subnet one and lets the admin override (matters
   // on multi-NIC hosts). See net.ts / wiki/concepts/device-input-flow.md.