Update all documentation to reflect new multi-network auto-detection
feature that scans all network interfaces (WiFi, Ethernet, VLANs,
bridges) across all tools.

Changes:
- README.md: Updated examples for tmp117-scan, scpi-client,
  and update-firmware to show auto-detection usage
- CHANGELOG.md: Added [Unreleased] section with multi-network
  auto-detection, file deletion, and 10-12x performance improvements
- DEVICE_SCANNER.md: Updated overview, quick start examples, and
  troubleshooting to reflect multi-network capability

Features documented:
- Auto-detection across all network interfaces (no IP needed)
- 10-12x faster OTA uploads (50-100 KB/s)
- File deletion support for git-aware deployment
- 97% bandwidth savings on incremental updates

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>