Wi-Fi over USB tab for firmware with the USB console (v13)

Writes / reads / removes the box's Wi-Fi over the serial port with the
usb_console commands (kota ping, wifi set|get|clear, health) and follows
the box through the restart until it joins the network. The password is
sent hex-encoded and never logged.

firmware/ now holds merged-binary-v13.bin (build 3ae273ec) instead of the
previous 1.0.16 build; error_ids.csv synced with the firmware.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_ui.py

@@ -0,0 +1,19 @@
+"""The whole window builds (catches errors that only show when the app starts)."""
+
+import os
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+
+def test_main_window_builds_with_all_tabs():
+    from PySide6.QtWidgets import QApplication
+
+    from kota_tech.ui.main_window import MainWindow
+    app = QApplication.instance() or QApplication([])
+    w = MainWindow()
+    tabs = w.centralWidget()
+    assert [tabs.tabText(i) for i in range(tabs.count())] == \
+        ["Quick start", "Serial monitor", "Flash firmware", "Wi-Fi (USB)", "SD card"]
+    assert not w.wifi_tab.write_btn.isEnabled()          # nothing connected, nothing typed
+    w.serial_tab.shutdown()
+    app.processEvents()