feat: let a companion app opt into the full RX log over BLE (#256)

Since beta_23 the per-packet RX log (PUSH_CODE_LOG_RX_DATA, 0x88) is kept off
BLE, because it floods a ~16 frame/sec link and starves chat and admin traffic
(#46, #54). That is still the right default and is unchanged here.

But it is also the ONLY frame carrying the transport codes and the full relay
path — RESP_CODE_CHANNEL_MSG_RECV_V3 has neither — so coverage and region
mapping apps have had no way to reconstruct either over BLE. @marcelverdult,
who writes KiekR, traced this through our source and asked for an opt-in rather
than a revert.

A companion can now request it per session:

    CMD_SET_CUSTOM_VAR   "ble.rxlog:1"     (and "ble.rxlog:0" to stop)

Chosen over a user-facing setting because the tradeoff belongs to the app, not
the user: an app that wants the firehose knows it wants it, and nobody else
should have to understand the question.

Deliberately NOT persisted. A stored flag would silently reinstate the #46/#54
flood for someone who tried a coverage app once and moved on — on the one link
that cannot absorb it. Asking again after each connect is cheap for an app and
is the safe default for everyone else.

The existing #94 one-shot (echoes of our own sends, so "Repeats heard" keeps
working) is untouched and still applies when the firehose is off.

Builds on T-Deck, V4 and Pager.

Requested by @marcelverdult.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/MyMesh.cpp

@@ -4559,6 +4559,20 @@ void MyMesh::handleCmdFrame(size_t len) {
     char *np = strchr(sp, ':'); // look for separator char
     if (np) {
       *np++ = 0; // modify 'cmd_frame', replace ':' with null
+      // #256: "ble.rxlog:1" opts THIS session's BLE companion into the full
+      // per-packet RX log (0x88). It is not a sensor setting, so intercept it
+      // before the sensor dispatch below. Coverage/region apps need it because
+      // the transport codes and the full relay path exist only in that frame —
+      // RESP_CODE_CHANNEL_MSG_RECV_V3 carries neither. Off by default and never
+      // persisted, so the #46/#54 fix stands for everyone who does not ask.
+      // Requested by the KiekR author (marcelverdult), who traced it for us.
+#if defined(ESP32) && defined(MULTI_TRANSPORT_COMPANION)
+      if (strcmp(sp, "ble.rxlog") == 0) {
+        MultiTransportCompanionInterface::bleSetRxLogFirehose(np[0] == '1');
+        writeOKFrame();
+        return;
+      }
+#endif
       bool success = sensors.setSettingValue(sp, np);
       if (success) {
         #if ENV_INCLUDE_GPS == 1