tune(repeater): default local advert interval 2min -> 6min

advert_interval defaulted to 1 (the field is minutes/2, so 2 minutes) --
too chatty for a repeater sitting on a desk being demoed/deployed. Field
only stores even minute counts, so 6 (value 3) is the closest step down
from "beeps too often" without landing under-target at 4.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018iubftDmKNWmkNnhJRz8UH

examples/simple_repeater/MyMesh.cpp

@@ -900,7 +900,7 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   _prefs.bw = LORA_BW;
   _prefs.cr = LORA_CR;
   _prefs.tx_power_dbm = LORA_TX_POWER;
-  _prefs.advert_interval = 1;        // default to 2 minutes for NEW installs
+  _prefs.advert_interval = 3;        // default to 6 minutes for NEW installs (field is minutes/2, no odd values)
   _prefs.flood_advert_interval = 47; // 47 hours
   _prefs.flood_max = 64;
   _prefs.flood_max_unscoped = 64;

examples/simple_repeater/main.cpp

@@ -51,7 +51,7 @@ extern "C" EMSCRIPTEN_KEEPALIVE int sim_is_ready() {
 
 // Same idea as companion_radio's sim_test_advert_flood() -- MyMesh's own
 // updateAdvertTimer() (called once from begin()) doesn't fire the repeater's
-// first self-advert for a full 2 minutes (advert_interval defaults to 1,
+// first self-advert for a full 6 minutes (advert_interval defaults to 3,
 // scaled *2*60*1000ms -- see MyMesh::updateAdvertTimer()/begin() in this
 // same MyMesh.cpp), so a host page that wants hero/B to discover the
 // repeater as a contact immediately on boot (rather than waiting out that