Phase 2: Add platform, channels, core_version to virtual emulator and OTA endpoint

Add comprehensive documentation for virtual device emulator ...

- tools/virtual_devices/README.md: full user guide with CLI, curl, Web UI
- docs/virtual-device-emulator.md: architecture docs with end-to-end example
- docs/architecture.md: mention virtual emulator in device section
- CLAUDE.md: add virtual-device-emulator.md to key files table

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
🤖 Generated with [Claude Code](https://claude.com/claude-code)

Add virtual device emulator (Flask) for relay and button types ...

- New tools/virtual_devices/ with Flask emulator, CLI, and web UI
- Supports relay (4 ch, set_state) and button (4 ch, click events)
- CLI: create, start, stop, list, status, click, remove, register
- Emulates full device REST contract: /about, /status, /action, /set_token, /reset, /channels_schema
- Web UI for visual control and monitoring
- Integrate with server registration via /api/v1/devices/setup/new-device
- Allow IP:port in setup_new_device validation for virtual devs

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
🤖 Generated with [Claude Code](https://claude.com/claude-code)