Serial monitor redesign: Test box button, InfluxDB row in the checklist

- Test box: restart + start-up capture + online InfluxDB check (data newer
  than the restart), with a status strip; checklist and findings are the
  main view, live log / guided troubleshooting / box details are tabs,
  rarely used actions in a More menu
- light palette on all systems (macOS dark mode made the colours unreadable)
- new rule influx.invalid_value: -inf from a silent microphone makes
  InfluxDB reject every upload (HTTP 400); guide end names it
- exclusive serial port on macOS/Linux: two tool windows no longer split
  the log between them
- InfluxDB check: `since` filter, neutral wording when nothing new arrives

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

tests/test_ui.py

@@ -19,3 +19,34 @@ def test_main_window_builds_with_all_tabs():
     assert "InfluxDB access..." in settings
     w.serial_tab.shutdown()
     app.processEvents()
+
+
+def test_serial_tab_checklist_and_test_strip():
+    from PySide6.QtWidgets import QApplication
+
+    from kota_tech.core.logline import parse_line
+    from kota_tech.service import influx
+    from kota_tech.ui.main_window import INFLUX_ROW, MainWindow
+    app = QApplication.instance() or QApplication([])
+    w = MainWindow()
+    st = w.serial_tab
+    assert st.test_btn.text().endswith("Test box")
+    assert [st.side_tabs.tabText(i) for i in range(st.side_tabs.count())] == \
+        ["Live log", "Guided troubleshooting", "Box details"]
+    st.influx_config = lambda: None                              # no token (never touch real settings)
+    rows = st._cloud_rows()
+    assert rows[0][0] == "off" and "not set up" in rows[0][1]
+    st.influx_config = lambda: influx.InfluxConfig("t")          # pretend access is set up
+    assert st._cloud_rows()[0] == ("pending", f"{INFLUX_ROW} - press Test box")
+    st._on_influx(influx.InfluxCheck(influx.SENSORS_MISSING, "Status arrives, sensor data does not",
+                                     details=["SEN66 (air quality): no data"]))
+    rows = st._cloud_rows()
+    assert rows[0][0] == "bad" and rows[1][0] == "note"
+    st._engine.feed(parse_line("ESP-ROM:esp32s3-20210327"))
+    st._diag_dirty = True
+    st._refresh_diag()
+    texts = [st.diag.milestones.item(i).text() for i in range(st.diag.milestones.count())]
+    assert any(INFLUX_ROW in t for t in texts)
+    assert "Test box" in st.test_status.text()
+    st.shutdown()
+    app.processEvents()