feat: remote commands, systemd units, process observability, broker auth split

- Command intake (reboot/shutdown) on infoscreen/{uuid}/commands with ack lifecycle
- MQTT_USER/MQTT_PASSWORD_BROKER split from identity vars; configure_mqtt_security() updated
- infoscreen-simclient.service: Type=notify, WatchdogSec=60, Restart=on-failure
- infoscreen-notify-failure@.service + script: retained MQTT alert when systemd gives up (Gap 3)
- _sd_notify() watchdog keepalive in simclient main loop (Gap 1)
- broker_connection block in health payload: reconnect_count, last_disconnect_at (Gap 2)
- COMMAND_MOCK_REBOOT_IMMEDIATE_COMPLETE canary flag with safety guard
- SERVER_TEAM_ACTIONS.md: server-side integration action items
- Docs: README, CHANGELOG, src/README, copilot-instructions updated
- 43 tests passing

scripts/start-simclient.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+# Start Simclient - MQTT communication and event intake for infoscreen
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(dirname "$SCRIPT_DIR")"
+VENV_PATH="$PROJECT_ROOT/venv"
+SIMCLIENT="$PROJECT_ROOT/src/simclient.py"
+
+echo "📡 Starting Simclient..."
+echo "Project root: $PROJECT_ROOT"
+
+# Check if virtual environment exists
+if [ ! -d "$VENV_PATH" ]; then
+    echo "❌ Virtual environment not found at: $VENV_PATH"
+    echo "Please create it with: python3 -m venv venv"
+    exit 1
+fi
+
+# Activate virtual environment
+source "$VENV_PATH/bin/activate"
+
+# Check if simclient.py exists
+if [ ! -f "$SIMCLIENT" ]; then
+    echo "❌ Simclient not found at: $SIMCLIENT"
+    exit 1
+fi
+
+ENV="${ENV:-development}"
+echo "Environment: $ENV"
+
+echo "Starting simclient..."
+echo "---"
+exec python3 "$SIMCLIENT"