Checklist: verify that sensor data reaches InfluxDB

New guided check "Sensor data in the database (InfluxDB)", also the last
step of the Quick check on the green path. It queries InfluxDB (read
token) for the newest point per measurement of the box and tells apart:
sensor data arrives / status arrives without sensor data / offline now /
never seen / check not possible. Polls every 30 s for up to 4 minutes.
With a stopped RTC in the log it concludes that sensor readings are lost
(stamped 1 Jan 2000): box A4:CB:8F:C9:47:3C sent only device_status and
microphone.

- service/influx.py: query, CSV parsing, classification (no new deps)
- guides: new step type "influx" (host answers via influx_result)
- Settings > InfluxDB access (or KOTA_INFLUX_TOKEN); token never logged
- service status mapping for tech.influx.* findings

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

tests/test_ui.py

@@ -15,5 +15,7 @@ def test_main_window_builds_with_all_tabs():
     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
+    settings = [a.text() for m in w.menuBar().actions() for a in m.menu().actions()]
+    assert "InfluxDB access..." in settings
     w.serial_tab.shutdown()
     app.processEvents()