feat: Add BLE RSSI room mapper example.

[nedseb]

Target repository

This example should be created in micropython-steami-sample, not in micropython-steami-lib. BLE examples are not tied to a specific driver and belong in the sample repo.

What

Create an example that records RSSI measurements at different positions in a room. The user moves around with the scanner board and presses a D-PAD button to log the RSSI of visible beacons at each position. Data is saved as CSV via daplink_flash.

Why

Fourth step in the BLE + indoor localization path. Builds the dataset needed for indoor positioning. Teaches data collection methodology and the relationship between physical position and signal strength.

Suggested approach

1. Place 2-3 beacon boards at known positions in a room
2. Scanner board scans all beacons and displays their names + RSSI on the OLED
3. User presses D-PAD RIGHT to record a measurement point
4. OLED shows the point number and number of beacons seen
5. Data is written to a CSV file via daplink_flash (columns: point_id, beacon_name, rssi)
6. Press D-PAD LEFT to stop and save

Learning goals

• Experimental data collection methodology
• Understanding RSSI variability (same position gives different readings)
• File I/O on MicroPython via DAPLink flash
• Introduction to the concept of a "radio fingerprint" of a position

Hardware

• 3-4 STeaMi boards (2-3 beacons + 1 scanner)
• SSD1327 OLED + D-PAD + DAPLink flash on scanner board

Depends on

• feat: Add BLE RSSI proximity detector example. #410 (RSSI proximity — reuse scanning logic)

Documentation

Write a pedagogical activity sheet for the STeaMi wiki covering:

• Learning objectives (data collection, RSSI variability, radio mapping)
• Room setup instructions (where to place beacons, grid layout)
• How to retrieve and analyze the CSV data
• Visualization suggestions (heatmap, scatter plot)