Merge mcarper/keymindCascade into mqtt-observer-plus

Integrates Mike Carper's transmission-reliability work (direct retries with
SNR-adaptive backoff and CR, flood retry controls, alt-path replies, flood
channel gates) plus its upstream/dev base (as of 2026-07-06) on top of the
observer stack. The flex branch is untouched; this branch is the experimental
integration line.

Conflict-resolution decisions, for future re-syncs (git rerere is enabled and
has recorded these):
- NodePrefs adopts keymind/upstream member order + retry/flood tail. Member
  order is in-memory only: /com_prefs stays field-by-field with the same
  canonical file order both sides already share through offset 294; keymind
  appends the retry tail at 295+ (new canonical size 676). Flex fleet files
  load unchanged; retry fields default via direct_retry_prefs_magic.
- loadPrefsInt keeps the fork's legacy MQTT-gap recovery but moves its
  detection boundary from 'extra > 5' to 'extra > LEGACY_MQTT_GAP_3SLOT (864)'
  so keymind-size tails take the normal read path. COM_PREFS_TAIL_BYTES
  retired.
- Dispatcher/RadioLibWrappers: fork watchdog additions + keymind TX overrides
  and CAD busy counter are unioned; RxReservePacketManager::queueOutbound
  follows upstream's new bool return (false when shedding).
- CommonCLI: fork observer dispatch + versioned /mqtt_prefs machinery kept;
  keymind CLI (retry/flood/radioat) taken; duplicate CAD/FEM handlers and
  sanitise lines deduped (kept keymind placements to minimize future diff).
- MyMesh (repeater/room): fork alerter/OTA/observer wiring kept; keymind
  scheduled-radio system replaces the old pending_* temp-radio members;
  applySavedRadioParams() replaces raw setParams at startup.
- ESP32Board: fork manifest-OTA + keymind powerOff/deepSleep and stopOTAUpdate
  unioned; startOTAUpdate keeps fork's STA-aware IP with keymind's idempotency
  guard.
- build.sh taken wholesale from keymind (fleet builds use GH Actions).

Verified: Heltec_v3_repeater_observer_mqtt, Heltec_v3_repeater,
heltec_v4_repeater_observer_mqtt, Heltec_v3_room_server_observer_mqtt build;
host migration harness (13 MQTT + non-MQTT scenarios) passes with updated
expectations (676-byte /com_prefs; odd-size files normalize on save, not
load); native unit tests 13/13.

examples/simple_sensor/SensorMesh.cpp

@@ -327,6 +327,9 @@ uint32_t SensorMesh::getDirectRetransmitDelay(const mesh::Packet* packet) {
 int SensorMesh::getInterferenceThreshold() const {
   return _prefs.interference_threshold;
 }
+bool SensorMesh::getCADEnabled() const {
+  return _prefs.cad_enabled;
+}
 int SensorMesh::getAGCResetInterval() const {
   return ((int)_prefs.agc_reset_interval) * 4000;   // milliseconds
 }
@@ -729,6 +732,7 @@ SensorMesh::SensorMesh(mesh::MainBoard& board, mesh::Radio& radio, mesh::Millise
   _prefs.flood_advert_interval = 0;   // disabled
   _prefs.disable_fwd = true;
   _prefs.flood_max = 64;
+  _prefs.flood_channel_data_enabled = 1;
   _prefs.interference_threshold = 0;  // disabled
   _prefs.radio_fem_rxgain = 1;        // LoRa FEM RX gain on by default (FEM boards)
   _prefs.cad_enabled = 0;             // hardware CAD before TX (off by default; 'set cad on')
@@ -737,6 +741,7 @@ SensorMesh::SensorMesh(mesh::MainBoard& board, mesh::Radio& radio, mesh::Millise
   _prefs.gps_enabled = 0;
   _prefs.gps_interval = 0;
   _prefs.advert_loc_policy = ADVERT_LOC_PREFS;
+  _prefs.radio_fem_rxgain = 1;
 
   memset(default_scope.key, 0, sizeof(default_scope.key));
 }