Add missing pyyaml dependency for FluidNC config

fluidnc_config.py imports yaml but pyyaml was not in requirements.txt,
causing 500 errors on calibration wizard commands.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

requirements.txt

@@ -13,6 +13,7 @@ websockets>=11.0.3  # Required for FastAPI WebSocket support
 requests>=2.31.0
 Pillow
 aiohttp
+pyyaml>=6.0
 # GPIO/NeoPixel support for DW LEDs and Desert Compass
 # Note: rpi-lgpio is a drop-in replacement for RPi.GPIO that works on Pi 5
 # Do NOT install both RPi.GPIO and rpi-lgpio - they conflict