v0.2.0

core: expose ids on shared entities, bare buttons, add TCOOLTHRS

Prep for products consuming valar-core as a remote package and overriding via
!extend (proven mechanism):
- add ids to the shared entities products rename/override: btn1/btn2/btn3,
  num_speed/num_accel/num_irun/num_tcoolthrs/num_sgthrs, sel_direction,
  sen_sgresult/sen_tstep
- buttons are now BARE (pins + debounce only); behaviour moves to the
  product/board layer, attached via !extend. Generic board buttons report state
  with no default action.
- add a shared TCOOLTHRS number (both products expose it)

Validated: esphome config passes on val3000/val3100/val3101.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XpCz2RvuxV5uV8bFwCEpkL