Add .env.template with placeholders (remove sensitive info)

.env.template

@@ -0,0 +1,38 @@
+# Infoscreen Client configuration template
+# Copy this file to .env and fill in values appropriate for your environment.
+
+# Environment
+ENV=development      # development | production
+DEBUG_MODE=0         # 1 to enable debug mode
+LOG_LEVEL=INFO       # DEBUG | INFO | WARNING | ERROR
+
+# MQTT Broker Configuration
+# Replace with your MQTT broker hostname or IP. Do NOT commit real credentials.
+MQTT_BROKER=<your-mqtt-broker-host-or-ip>
+MQTT_PORT=1883
+
+# Timing Configuration (seconds)
+HEARTBEAT_INTERVAL=60
+SCREENSHOT_INTERVAL=180
+DISPLAY_CHECK_INTERVAL=15
+
+# File/API Server (used to download presentation files)
+# If event URLs use host 'server', the client rewrites them to this server.
+# You can either set FILE_SERVER_BASE_URL (preferred) or FILE_SERVER_HOST+PORT+SCHEME.
+FILE_SERVER_HOST=
+FILE_SERVER_PORT=8000
+FILE_SERVER_SCHEME=http
+# FILE_SERVER_BASE_URL=http://<your-file-server-host>:8000  # optional, takes precedence
+
+# Optional: MQTT authentication (if your broker requires username/password)
+#MQTT_USERNAME=
+#MQTT_PASSWORD=
+
+# Optional TLS settings (if using secure MQTT)
+#MQTT_TLS_CA_CERT=
+#MQTT_TLS_CERT=
+#MQTT_TLS_KEY=
+
+# Notes:
+# - Keep actual secrets and host-specific values in a local .env file that is NOT committed.
+# - This template is safe to check into version control.