fix(esp32): suppress ESP-IDF info logs and switch BLE stack to Bluedroid

Two reports rolled into one sdkconfig change:

1. Beta testers reported "weird serial output" across DHT22, Servo+Pot,
   Joystick, WiFi×2, and DualADC examples. The user's Serial.print lines
   came interleaved with internal ESP-IDF chatter:

       I (53306) gpio: GPIO[4]| InputEn: 1| OutputEn: 0| ...
       I (10626) phy_init: phy_version 4791,2c4672b,...

   sdkconfig.defaults didn't pin a default log level so it inherited
   CONFIG_LOG_DEFAULT_LEVEL_INFO. Set WARN (level 2) so only warnings
   and errors leak into the user's serial output. Sketches can still
   esp_log_level_set() per tag at runtime if they want verbose.

2. BLE Advertise example failed to compile. sdkconfig had NimBLE
   enabled, but arduino-esp32 2.0.17's BLEDevice.h targets Bluedroid.
   Switch the stack: enable BT_BLUEDROID + BTDM_CTRL_MODE_BR_EDR_BLE +
   BT_BLE so the standard arduino-esp32 BLE library compiles. Sketches
   that explicitly include NimBLEDevice.h will not compile under this
   config — that's a smaller minority than the BLEDevice.h users.

The runtime side of BLE still depends on stubs in the qemu-lcgamboa
fork; this only fixes the compile path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/services/esp-idf-template/sdkconfig.defaults

@@ -9,6 +9,12 @@ CONFIG_ESPTOOLPY_FLASHSIZE_4MB=y
 # Bootloader — minimal logging to speed up QEMU boot
 CONFIG_BOOTLOADER_LOG_LEVEL_NONE=y
 
+# Default log level — WARN so users see only their Serial.print + real warnings.
+# Internal ESP-IDF info-level chatter (gpio:, wifi:, phy:) is suppressed.
+# Override per-tag with esp_log_level_set() at runtime if needed.
+CONFIG_LOG_DEFAULT_LEVEL_WARN=y
+CONFIG_LOG_DEFAULT_LEVEL=2
+
 # Watchdogs — disable for QEMU (timing is not real-time)
 CONFIG_ESP_TASK_WDT=n
 CONFIG_ESP_INT_WDT=n
@@ -38,6 +44,10 @@ CONFIG_ESP_MAIN_TASK_STACK_SIZE=8192
 # Enable C++ exceptions (some Arduino libraries require it)
 CONFIG_COMPILER_CXX_EXCEPTIONS=y
 
-# Bluetooth for BLE examples
+# Bluetooth for BLE examples — Bluedroid stack (the default arduino-esp32
+# BLEDevice.h library targets Bluedroid, not NimBLE). NimBLE-based sketches
+# (NimBLEDevice.h) will not compile under this config; flip stacks if needed.
 CONFIG_BT_ENABLED=y
-CONFIG_BT_NIMBLE_ENABLED=y
+CONFIG_BT_BLUEDROID_ENABLED=y
+CONFIG_BTDM_CTRL_MODE_BR_EDR_BLE=y
+CONFIG_BT_BLE_ENABLED=y