OTAFIX 2.4.1 Preview 4 - reliable BLE DFU

Preview 4 improves BLE DFU reliability with phone-controlled connection updates, a 15-30 ms preferred interval, zero slave latency, and a 4-second supervision timeout. It recommends PRN 8 and aligns Make optimization flags so all 15 boards build successfully. Validation: tools/build_all.py passed 15/15 boards.