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>

kota_tech/diag/guides.toml

@@ -750,12 +750,18 @@ type = "influx"
 text = "Checking in InfluxDB that this box's data arrives: device status, microphone and the sensors (AS7341, BME688, SEN66). Keep the box switched on and online. The tool checks again every 30 s for up to 4 minutes (the air sensor needs about 2 minutes after a restart). The laptop needs Internet for this check."
 timeout_s = 240
 poll_s = 30
-outcomes = { ok = "end:data_ok", sensors_missing = "why", silent = "end:silent", never = "end:never", unavailable = "end:unavailable" }
+outcomes = { ok = "end:data_ok", sensors_missing = "why", silent = "why_silent", never = "why_silent", unavailable = "end:unavailable" }
+
+[[guide.step]]
+id = "why_silent"
+type = "route"
+routes = { "influx.invalid_value" = "end:invalid_value" }
+default = "end:silent"
 
 [[guide.step]]
 id = "why"
 type = "route"
-routes = { "kota.rtc_stopped" = "end:sensors_clock", "rtc.clock_not_running" = "end:sensors_clock", "kota.rtc_not_ticking" = "end:sensors_clock", "kota.time_invalid" = "end:sensors_clock", "kota.rtc_read_failed" = "guide:rtc_i2c", "rtc.init_failed" = "guide:rtc_i2c", "sensor.init_failed" = "guide:sensors", "kota.sensor_missing" = "guide:sensors" }
+routes = { "influx.invalid_value" = "end:invalid_value", "kota.rtc_stopped" = "end:sensors_clock", "rtc.clock_not_running" = "end:sensors_clock", "kota.rtc_not_ticking" = "end:sensors_clock", "kota.time_invalid" = "end:sensors_clock", "kota.rtc_read_failed" = "guide:rtc_i2c", "rtc.init_failed" = "guide:rtc_i2c", "sensor.init_failed" = "guide:sensors", "kota.sensor_missing" = "guide:sensors" }
 default = "end:sensors_missing"
 
 [[guide.end]]
@@ -765,6 +771,16 @@ title = "Box is healthy and its sensor data reaches InfluxDB"
 text = "Status, microphone and all sensor readings of this box arrived in InfluxDB in the last 15 minutes."
 actions = []
 
+[[guide.end]]
+id = "invalid_value"
+severity = "critical"
+title = "InfluxDB rejects every upload of this box (invalid value -inf)"
+text = "The box is online and uploads, but one measurement carries -inf (the microphone records pure silence). InfluxDB refuses the whole upload with HTTP 400, so neither the status nor the sensor data arrive."
+actions = [
+  "Run the Microphone check: a working microphone (and its switch ON) avoids the -inf value.",
+  "Save the session log and send it to the firmware team: the firmware must skip invalid values.",
+]
+
 [[guide.end]]
 id = "sensors_clock"
 severity = "error"