components/sud.py: adds SudState.PAUSED. pause() freezes RAMPING/
HOLDING (the hold countdown and ramp-reached checks both no-op while
PAUSED, since they're gated on the exact state they froze); start()
now doubles as resume when paused. stop() aborts back to IDLE from
any in-progress state, reusing the same reset logic as __init__/
upload() (factored into _reset_run_state()).
tasks/sud.py: maps 'Pause'/'Stop' messages to the new methods, and
turns the stirrer off on IDLE (not just DONE) so stop() actually
silences it instead of leaving the last step's stirring running.
client/brewpi_gui.py: wires the Pause/Stop toolbar actions, extends
update_sud_actions() so Start doubles as Resume and Stop stays usable
while paused, and freezes the forecast plot's progress line for the
duration of a pause (tracked via accumulated paused time) instead of
letting it drift ahead of actual progress.