Give up the radio for the link, not for the search

Two failures on the tablet, one of them mine from an hour ago.

The real one first. A trainer that drops mid-ride could not get back:
its supervisor reconnects on its own (FR-1.10) and those attempts never
pass through `DeviceRegistry::connect`, so nothing suspended the device
list for them. On Android a GATT link that is discovering services while
a scan is running is killed by the platform, and the log has it exactly —
a reconnect at 13:07:18 dying with `Disconnected while discovering
services`, inside a list-scan session opened at 13:07:02.

My first fix was to suspend the list whenever the trainer was
mid-connect. That was drawn around the wrong thing. `Connecting` covers
the 15 s *search*, `Reconnecting` covers the backoff between attempts,
and against an asleep trainer those alternate for the whole of
RECONNECT_ATTEMPTS — so the list scan went off the air for minutes and
every other device starved with it. A pod that dropped could never be
seen again, which is what "the pods disconnect after 40 seconds" was.

The window that matters is narrower than either: connect, then discover
services. `scan::gatt_setup` marks it — an RAII guard taken by the
trainer, pod and heart rate paths the moment their search returns a
peripheral — and the device list yields only for that. Measured on the
tablet: 1.2 s of yielding for a heart rate connect, then straight back to
one session per 21 s.

Also: the "+ pod seen; the − pod speaks for the pair" line is logged once
per run of refusals rather than once per sighting. The device list
republishes several times a second and every pass re-reported a visible
pod — 274 identical lines in five minutes, burying the connect failures
the log was being read for.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "BikeControl",
-  "version": "0.2.1",
+  "version": "0.2.3",
   "identifier": "paris.tourolle.bikecontrol",
   "build": {
     "frontendDist": "../ui/dist",
@@ -43,7 +43,7 @@
     ],
     "category": "Utility",
     "android": {
-      "versionCode": 1201
+      "versionCode": 1203
     },
     "shortDescription": "Indoor cycling trainer control",
     "longDescription": "Control a smart trainer over BLE, ride gradient profiles and synthetic waveforms, and record the result."