fix(firmware): upgrade NimBLE to 2.x + DNS fallback for unreliable resolvers

NimBLE-Arduino 1.4.2 had an init/fire race in its FreeRTOS callout porting
layer where os_callout_timer_cb dispatched a queued TimerHandle expiry
against a not-yet-initialized event (NULL fn pointer), causing PC=0
InstrFetchProhibited within ~1s of boot when the camera task starved the
timer service. Confirmed by ets_printf instrumentation. Upgrading to
^2.0.0 rewrites the porting layer and eliminates the race; verified clean
on the customer network for 1+ hour.

Also rolls in DNS-resilience work that surfaced the BLE crash during
provisioning: pin lwIP/esp-netif resolvers to 1.1.1.1/8.8.8.8 across DHCP
renewals, add three-tier resolver fallback in reporter with a hardcoded
IP of last resort, and switch to raw WiFiClient with manual Host header
to bypass HTTPClient's brittle DNS path.

Migration touches for NimBLE 2.x:
- NimBLEAdvertisedDeviceCallbacks -> NimBLEScanCallbacks
- onResult signature now takes const NimBLEAdvertisedDevice*
- setAdvertisedDeviceCallbacks -> setScanCallbacks
- start(0, nullptr, false) -> start(0, false, false)

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

firmware/platformio.ini

@@ -21,7 +21,7 @@ upload_flags = --no-stub
 lib_deps =
     tzapu/WiFiManager@^2.0.17
     bblanchon/ArduinoJson@^7.0.0
-    h2zero/NimBLE-Arduino@^1.4.2
+    h2zero/NimBLE-Arduino@^2.0.0
     espressif/esp32-camera
 
 ; Frame-capture build. Strips WiFi/BLE/CV/reporter; streams raw 96x96 frames