Add idle auto-shutdown for self-hosted deployment

- IDLE_TIMEOUT_MINUTES env var to configure shutdown after inactivity
- Background thread monitors activity and exits when timeout reached
- Activity tracked via simulation_display fragment (runs while page open)
- Set to 0 (default) to disable auto-shutdown

src/py_dvt_ate/app/dashboard/app.py

@@ -7,6 +7,8 @@ thermal-electrical coupling in real-time using instrument interfaces.
 
 import asyncio
 import atexit
+import os
+import sys
 import threading
 import time
 from collections import deque
@@ -27,6 +29,41 @@ from py_dvt_ate.tests.thermal.tempco import TempCoTest
 # Thread pool for background test execution
 _test_executor = ThreadPoolExecutor(max_workers=1, thread_name_prefix="test_runner")
 
+# Idle shutdown configuration
+# Set IDLE_TIMEOUT_MINUTES=0 to disable auto-shutdown
+IDLE_TIMEOUT_MINUTES = int(os.environ.get("IDLE_TIMEOUT_MINUTES", "0"))
+_last_activity_time: float = time.time()
+_idle_monitor_started = False
+
+
+def _update_activity() -> None:
+    """Update the last activity timestamp."""
+    global _last_activity_time
+    _last_activity_time = time.time()
+
+
+def _idle_monitor() -> None:
+    """Background thread that exits the app after idle timeout."""
+    global _last_activity_time
+    while True:
+        time.sleep(60)  # Check every minute
+        if IDLE_TIMEOUT_MINUTES <= 0:
+            continue
+        idle_minutes = (time.time() - _last_activity_time) / 60
+        if idle_minutes >= IDLE_TIMEOUT_MINUTES:
+            print(f"Idle timeout reached ({IDLE_TIMEOUT_MINUTES} minutes). Shutting down.")
+            os._exit(0)
+
+
+def _start_idle_monitor() -> None:
+    """Start the idle monitor thread if timeout is configured."""
+    global _idle_monitor_started
+    if IDLE_TIMEOUT_MINUTES > 0 and not _idle_monitor_started:
+        _idle_monitor_started = True
+        thread = threading.Thread(target=_idle_monitor, daemon=True)
+        thread.start()
+        print(f"Idle auto-shutdown enabled: {IDLE_TIMEOUT_MINUTES} minutes")
+
 # History buffer size for charts
 HISTORY_SIZE = 500
 
@@ -124,6 +161,10 @@ def start_embedded_server() -> tuple[SimulationServer, threading.Thread]:
 
 def init_session_state() -> None:
     """Initialise Streamlit session state."""
+    # Start idle monitor for auto-shutdown
+    _start_idle_monitor()
+    _update_activity()
+
     if "server" not in st.session_state:
         with st.spinner("Starting simulation server..."):
             st.session_state.server, st.session_state.server_thread = start_embedded_server()
@@ -386,6 +427,8 @@ def display_controls() -> None:
 @st.fragment(run_every=0.1)
 def simulation_display() -> None:
     """Fragment that displays and updates simulation state."""
+    _update_activity()  # Track that someone is viewing the dashboard
+
     if "server" not in st.session_state:
         st.warning("Initializing simulation server...")
         return