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_guides.py

@@ -334,3 +334,15 @@ def test_quick_check_green_ends_with_influx_check(influx_rig):
     runner.answer("GREEN")
     runner.answer("0")                           # heartbeat blinking
     assert runner.guide.id == "influx" and actions == ["influx"]
+
+
+def test_influx_rejected_upload_is_named(influx_rig):
+    engine, runner, clock, actions, board = influx_rig
+    board(*BOOT, "microphone,device=A4CB8FC9473C dbfs=-inf,db=-inf 1790805114000000000",
+          "io,device=A4CB8FC9473C dbfs=-inf,db=-inf 1790805215000000000")   # USB dropped characters
+    assert sum(k.startswith("influx.invalid_value") for k in engine.findings) == 1
+    runner.start("influx")
+    runner.influx_result("silent", "No new data in InfluxDB since the test started")
+    clock.t += 300
+    runner.tick()
+    assert runner.end.id == "invalid_value"