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/rules.toml

@@ -280,6 +280,20 @@ severity = "warning"
 title = "InfluxDB refused some measurements (HTTP 400)"
 meaning = "A measurement was malformed and dropped (firmware issue, not a hardware fault)."
 actions = ["Save the session log and send it to the firmware team."]
+explained_by = ["influx.invalid_value"]
+
+[[rule]]
+id = "influx.invalid_value"
+# Line protocol printed by SENSOR_GATHERER / INFLUX: "-inf"/"nan" are not valid
+# numbers, and one bad line makes InfluxDB reject the whole upload.
+pattern = '^(?:.*format: )?(?P<measurement>[a-z0-9_]+),device=\S+ \S*=-?(?:inf|nan)\b'
+severity = "critical"
+title = "Box sends an invalid value (-inf/nan) - InfluxDB rejects all its data"
+meaning = "A measurement contains -inf or nan (the microphone: pure silence gives -inf dB). InfluxDB refuses the whole upload with HTTP 400, so status and sensor data from this box are lost too. Firmware bug; a silent microphone triggers it."
+actions = [
+  "Check the microphone (Microphone check): a working microphone avoids the -inf value.",
+  "Save the session log and send it to the firmware team: invalid values must be skipped, not uploaded.",
+]
 
 [[rule]]
 id = "influx.env_missing"
@@ -713,7 +727,7 @@ actions = [
   "Check the network has Internet (open a website on a phone on the same Wi-Fi).",
   "Check INFLUX_URL / INFLUX_TOKEN in ENV.TXT (re-provision the SD card).",
 ]
-explained_by = ["kota.time_invalid", "influx.auth", "influx.not_found", "status.conn.1", "net.dns_fail", "net.tls_fail", "influx.server_error"]
+explained_by = ["influx.invalid_value", "kota.time_invalid", "influx.auth", "influx.not_found", "status.conn.1", "net.dns_fail", "net.tls_fail", "influx.server_error"]
 
 [[rule]]
 id = "kota.low_heap"