Feat/ble rssi mapper.

[MatteoCnda1]

Summary

Add a BLE RSSI room mapper example using STM32duinoBLE. Closes #97

Changes

• Added lib/ble/examples/BleRssiMapper/BleRssiMapper.ino
• Scans up to 3 beacons simultaneously (Beacon_M1, Beacon_M2, Beacon_M3)
• Serial commands:
  • r → record current RSSI for all visible beacons as a CSV row
  • s → stop and print full CSV to Serial monitor
  • h → print help
• Moving average over 5 RSSI samples per beacon to reduce noise
• CSV stored in RAM (up to 50 points × 3 beacons) and printed on stop
• Note: D-PAD and DAPLink flash drivers not yet available in Arduino —
  Serial monitor used as fallback

Checklist

• make lint passes (clang-format)
• make build passes (PlatformIO)
• make test-native passes
• [ x] make test-hardware passes on a connected STeaMi
• [ x] README updated (if adding/changing public API)
• Examples added (lib/ble/examples/BleRssiMapper/BleRssiMapper.ino)
• Commit messages follow conventional commits format