Add build outputs to .gitignore

- Exclude build-output/ directory from version control
- Ignore binary files (.bin, .elf, .map)
- Keep source code and build artifacts separate

WeighMyBru² v2.1.0 - ESP32 Web Tools Integration

Complete browser-based firmware flashing with LittleFS filesystem support.

Features:
- ESP32 Web Tools browser-based flashing
- Complete 4-part flash: bootloader, partitions, firmware, filesystem
- LittleFS filesystem with full web interface (896KB)
- Support for ESP32-S3 Supermini and XIAO ESP32S3
- Professional flash page at weighmybru.com/flash
- No software installation required

Release files include firmware binaries, filesystem images, ESP32 Web Tools manifests, and comprehensive documentation.