Add BLE Wi-Fi provisioning alongside the setup SoftAP

Wraps ESP-IDF's official wifi_provisioning manager (BLE transport,
protocomm Security1, NimBLE host) so a phone can join the device to
Wi-Fi over the ESP32-S3's own onboard BLE radio, without first
connecting to the 192.168.4.1 SoftAP. Chosen over a custom GATT
service specifically so the existing generic "ESP BLE Provisioning"
iOS/Android apps work today, before the dedicated DigiRadio app
exists — same standard protocol either app would speak.

net::ble_provisioning::start() is additive, not a replacement: it
runs next to the current SoftAP + POST /api/wifi HTTP route inside
NetBootstrap's startSetupMode(), and failing to start it is
non-fatal (same pattern already used there for the SigmaStudio TCP
bridge) — SoftAP setup keeps working either way. Proof-of-possession
is the device's own serial number (same source as the SoftAP SSID),
so pairing requires reading it off the unit rather than being wide
open. On WIFI_PROV_CRED_SUCCESS the received wifi_sta_config_t is
converted to the same core::WifiCredentials type the HTTP handler
uses and saved through the same ISecureStore, then the device
reboots into STA mode — one persistence path regardless of which
transport provisioned it.

BT1035 is unaffected: it's a separate UART-attached classic
Bluetooth module for A2DP output. This uses the ESP32-S3's
independent internal BLE controller, switched to NimBLE (smaller
footprint than Bluedroid, the only host stack needed for a single
peripheral-role GATT service). App binary still has 33% free flash
after pulling in wifi_provisioning/protocomm/NimBLE.

Verified: idf.py build, doxygen (0 warnings), check-manual-sync,
check_si4684_blobs, ctest (19/19) all green. Not yet tested with a
real BLE provisioning app or on hardware — board is disconnected
this session.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0178rASQ6ZETPMUamvpoR2KR

Software/sdkconfig.defaults

@@ -28,3 +28,10 @@ CONFIG_COMPILER_CXX_STD=23
 CONFIG_LOG_DEFAULT_LEVEL_INFO=y
 CONFIG_ESPTOOLPY_FLASHSIZE_16MB=y
 CONFIG_ESP_MAIN_TASK_STACK_SIZE=8192
+
+# Onboard BLE for wifi_provisioning (net/BleProvisioning.cpp) — the ESP32-S3's
+# own radio, independent of the BT1035 UART module which stays classic-A2DP-only.
+# NimBLE instead of Bluedroid: smaller flash/RAM footprint, and the only host
+# stack this firmware needs is a single GATT peripheral role for provisioning.
+CONFIG_BT_ENABLED=y
+CONFIG_BT_NIMBLE_ENABLED=y