Add "UWB Follow-Me System"

UWB Follow-Me System.-.md

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+# UWB Follow-Me System
+
+## Overview
+Precision person-following using Ultra-Wideband (UWB) two-way ranging. Enables SaltyLab to follow Tee during outdoor EUC rides at 20-30 km/h.
+
+## Hardware
+### MaUWB ESP32-S3 (DW3000)
+- **Vendor:** Makerfabs
+- **URL:** https://www.makerfabs.com/mauwb-esp32s3-uwb-module.html
+- **Price:** $54.80 USD each
+- **SKU:** MAUWBS3CA1
+- **Qty needed:** 3 (1 tag + 2 anchors)
+
+### Specs
+| Parameter | Value |
+|-----------|-------|
+| UWB Chip | Qorvo DW3000 + PA |
+| MCU | ESP32-S3 (WiFi + BLE 5.0) |
+| Co-processor | STM32 (TWR scheduling firmware) |
+| Range | 500m outdoor |
+| Accuracy | ±10cm |
+| Max anchors | 8 (auto-select nearest) |
+| Max tags | 64 |
+| Interface | AT commands via UART, USB |
+| Display | 0.96\" OLED |
+| Power | USB 5V, ~200-250mA active |
+| Channels | UWB Ch5 (6.5 GHz) + Ch9 (8 GHz) |
+| Apple U1 | Interoperable (per Qorvo) |
+
+## System Layout
+```
+[Tag - on Tee]          [Anchor A - left stem]     [Anchor B - right stem]
+  MaUWB ESP32-S3          MaUWB ESP32-S3             MaUWB ESP32-S3
+  18650 battery            USB → Orin Nano            USB → Orin Nano
+  OLED shows range         ~25cm apart for bearing estimation
+```
+
+## How It Works
+1. **Tag** (Tee) and **Anchors** (bot) perform Two-Way Ranging (TWR) at ~10-100Hz
+2. STM32 firmware handles time-slot scheduling (no signal conflicts)
+3. ESP32-S3 reports range via AT commands over UART/USB
+4. Two anchors spaced 25cm apart → **TDoA gives bearing angle**
+5. ROS2 node publishes `/uwb/target` (distance + angle in base_link frame)
+6. Fused with camera person detection for identity confirmation
+
+## Tag Battery (12hr runtime)
+- 3000mAh 18650 cell (e.g., Samsung 35E)
+- TP4056 USB-C charger board
+- Mini boost converter to 5V
+- 3D-printed enclosure with belt clip
+
+## Software Integration
+- ROS2 package: `saltybot_uwb`
+- Subscribes to anchor serial ports
+- Publishes: `/uwb/target` (geometry_msgs/PoseStamped)
+- Fused in `person_follower_node` as primary position source
+- Camera serves as secondary (identity confirmation + obstacle avoidance)
+
+## References
+- Makerfabs GitHub: https://github.com/Makerfabs/Makerfabs-ESP32-UWB-DW3000
+- MaUWB AT command docs: https://www.makerfabs.com/blog/post/mauwb-new-firmware-upgrade_v112
+- Gitea issue: #57
+