Fix critical safety issue: Move ESP8266 heater control from GPIO16 to GPIO13

[Copilot]

GPIO16 on ESP8266 is HIGH during boot, causing the sauna heater to activate during startup or device hangs—a fire hazard.

Changes

• sauna_controller.yaml: Moved heater control from D0 (GPIO16) to D7 (GPIO13)
  • GPIO13 is LOW during boot, preventing unintended heater activation
  • Updated pin mapping comments
• README.md: Added safety warning about GPIO16 behavior on ESP8266

Hardware Impact

Users must rewire heater control from D0 to D7 on their ESP8266 board.

# Before (unsafe)
output:
  - platform: slow_pwm
    pin: D0  # GPIO16 - HIGH during boot
    id: sauna_ofen_pwm

# After (safe)
output:
  - platform: slow_pwm
    pin: D7  # GPIO13 - LOW during boot
    id: sauna_ofen_pwm

Fixes #2

Original prompt

gibt es offene bugs?

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