docs: rewrite ESP32_EMULATION.md with complete installation guide
Add step-by-step setup section (section 1) covering:
- MSYS2 installation and required packages
- arduino-cli + esp32:esp32@2.0.17 core install
- esptool installation
- Building libqemu-xtensa.dll from qemu-lcgamboa submodule
- Obtaining ESP32 ROM binaries
- Python venv + backend dependencies
- Verifying with test suite (28 + 13 tests)
- Running backend with ESP32 emulation active
- Compiling custom sketches for QEMU
Update section 11 (Frontend events): all events are now implemented
(gpio_change, ledc_update, ws2812_update, gpio_dir, i2c_event, spi_event,
system:crash/reboot) — removed "Pending" status, added ✅ for each.
Update section 10 (Tests): document both test suites with per-test table.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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