README: refresh docs for heater shutdown, resume fix, browser countdown

- HeaterTask.shutdown() on DONE/IDLE: document the _on_end callback,
  power-zero, TC disable, and ClosedLoop:false broadcast to clients.
- Resume with inherited temperature: document _paused_temp_soll fallback
  for steps that carry no temperature of their own.
- Browser client additional features: update Header countdown (now three
  rows: total/ramp/hold, always h:mm:ss) and describe the step-plate
  Ramp/Hold green countdown and configured hold-duration field.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SH2D4LRuCnhLSzoYerAfJX

README.md

@@ -347,9 +347,15 @@ in closed-loop mode (the default) and disabled in open-loop mode. This is
 wired up in `server/brewpi.py` via
 `heater_task.set_on_closed_loop_changed(tc.set_enabled)`, and fired once
 at startup from `HeaterTask.on_process()` so the TC is live immediately.
-`SudTask` no longer manages the TC's enabled state — its
+`SudTask` no longer manages the TC's enabled state directly; instead, when
-`on_state_changed()` only stops the stirrer when a run ends. See "Heater
+a run ends (state reaches `DONE` or `IDLE` — whether the schedule completed
-control modes" below.
+or Stop was pressed), it fires an `_on_end` callback that calls
+`HeaterTask.shutdown()`: this zeros `power_soll`, disables the TC, switches
+`closed_loop` to `False`, and broadcasts `{ClosedLoop: false}` to all clients
+so their checkboxes uncheck immediately. Re-enabling for manual use after a
+stop requires the user to check the Closed-loop checkbox again (or the
+next `Start` press does it automatically — see "Heater control modes"). See
+"Heater control modes" below.
 
 ### Heater control modes
 
@@ -380,7 +386,11 @@ browser tab is immediately reflected in every other connected client.
 On every resume from pause, `SudTask.recv()` restores the current step's
 schedule parameters (temperature setpoint, heat rate, stirrer) before the
 run continues, overwriting any manual adjustments the user made while
-paused.
+paused. Steps that carry no `temperature` of their own (`temperature=None`
+— they inherit whatever the previous step left the TC targeting) are
+handled via `_paused_temp_soll`: the setpoint is saved the moment Pause is
+pressed and restored as a fallback on resume, so the TC always snaps back
+to the correct target even for inherited-temperature steps.
 
 ### Forecast vs. actual duration
 
@@ -614,10 +624,21 @@ Additional features beyond the initial port:
   Sud is paused or stopped; auto-reset to Closed-loop on play. Slider
   enable/disable follows the mode: temperature setpoint and heat rate
   active in Closed-loop + not running; heater power active in Open-loop +
-  not running.
+  not running. When a run ends (DONE or Stop), `HeaterTask.shutdown()`
-- **Header countdown**: step remaining and total remaining timers,
+  fires automatically — the checkbox unchecks, power goes to 0, TC is
-  displayed in accent-coloured monospace next to the transport buttons,
+  disabled (see "Heater control modes" above).
-  derived from `forecast_step_starts`/`StepStarts`.
+- **Header countdown**: three monospace rows next to the transport buttons,
+  always in `h:mm:ss` format: *total* (time until the schedule finishes),
+  *ramp* (ramp phase remaining for the current step — total step span minus
+  the configured hold duration), and *hold* (`Sud.hold_remaining` pushed
+  live from the server). All three derive from `forecast_step_starts`/
+  `StepStarts`; "ramp" shows `0:00:00` once the hold phase begins.
+- **Step-plate countdowns**: each plate's top-right shows the remaining
+  ramp time in green digits. The active step overrides this with a "Ramp
+  h:mm:ss" or "Hold h:mm:ss" prefix (same element reused for both phases).
+  Configured hold duration (`hold.duration` formatted as `h:mm:ss`) is
+  shown as a static field on each plate; steps with no hold phase show
+  "Hold —".
 - **Controls always reflect server values**: sliders and readouts track
   every server push unconditionally — there are no "initial sync only"
   guards that could leave a control stale after a reconnect or while