server: always write log_{date_time}.json for the full server session

Adds ServerLogTask (tasks/server_log.py) which records temp/power samples
from startup to shutdown regardless of Sud state, in the same Name/Samples
JSON format as SudLogTask so analyze_log.py and replay_sim.py can consume
it directly.  The file is written on graceful exit (Ctrl-C) from brewpi.py's
finally block, just before the heater is closed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/brewpi.py

@@ -15,7 +15,7 @@ from components.plant import PlantFactory
 from components.actor import StirrerFactory
 from components.sud import Sud
 from components.sud_forecast import SudForecastEstimator
-from tasks import TaskManager, TempSensorTask, HeaterTask, PotTask, TcTask, StirrerTask, SudTask, SudLogTask
+from tasks import TaskManager, TempSensorTask, HeaterTask, PotTask, TcTask, StirrerTask, SudTask, SudLogTask, ServerLogTask
 
 import argparse as ap
 
@@ -140,6 +140,11 @@ if __name__ == '__main__':
 	# tasks/sud_log.py.
 	taskmgr.add(SudLogTask(sud, tc, heater, heater_task, sud_task, DT_TASK))
 
+	# Continuous server-session log - records from startup to shutdown
+	# regardless of Sud state; written to logs/log_{date_time}.json on exit.
+	server_log_task = ServerLogTask(tc, heater, heater_task, DT_TASK, args.logdir)
+	taskmgr.add(server_log_task)
+
 	# Assign data flow
 	# Assign tc control value to heater
 	tc.set_on_changed("y", heater_task.actor)
@@ -203,6 +208,7 @@ if __name__ == '__main__':
 			task.cancel()
 		if pending:
 			loop.run_until_complete(asyncio.gather(*pending, return_exceptions=True))
+		server_log_task.write()
 		# Belt-and-suspenders: explicitly close the heater connection even if
 		# the task cleanup above failed to reach HeaterHendi.activate(False).
 		heater.close()