Feat/ble trilateration.

[MatteoCnda1]

Summary

Add a BLE trilateration indoor positioning example using STM32duinoBLE. Closes #98

Changes

• Added lib/ble/examples/BleTrilateration/BleTrilateration.ino
• Scans 3 named beacons simultaneously (Beacon_M1, Beacon_M2, Beacon_M3)
• Converts RSSI to distance using per-beacon log-distance path loss model:
  • RSSI_ref at 1m: M1=-75, M2=-75, M3=-80
  • Path loss n: M1=3.99, M2=4.32, M3=2.66
• Trilaterates 2D position using least-squares circle intersection
• Multi-layer filtering pipeline:
  • Moving average over 8 RSSI samples per beacon
  • Distance clamped to 430cm
  • Trilateration result rejected if too far from centroid (>550cm)
  • Exponential smoothing (alpha=0.15) with 15cm minimum movement threshold
• Displays ASCII 2D map on Serial monitor (1 char = 10cm)
• Position updated every 500ms, map every 2s

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/BleTrilateration/BleTrilateration.ino)
• Commit messages follow conventional commits format