tc_constants.py only held States and DEFAULT_THRESHOLDS, both used
exclusively by temp_controller_base.py and its subclasses; fold them
into temp_controller_base.py directly and drop the now-empty module.
Also drop heat_diffusion.py, unused since pot.py switched to the
delay-line model, and the matching dead import in pot.py.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
[brewpi] - drop trace vars for the dtheta_ist_* attributes removed
when temp_controller_smith.py dropped Kalman filtering
[Pot] - drop unused kn field (never read since the noise-injection
code that used it was dropped)
[GUI] - default WS connection to ws://localhost:8765
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>