docker environment control improvement

APP_CORE/Dockerfile.api

@@ -1,3 +1,9 @@
+# APP_CORE API
+# Supported ENV overrides (Format: OVPMON_{SECTION}_{KEY}):
+# API: OVPMON_API_HOST, OVPMON_API_PORT, OVPMON_API_DEBUG, OVPMON_API_SECRET_KEY
+# MONITOR: OVPMON_OPENVPN_MONITOR_DB_PATH, OVPMON_OPENVPN_MONITOR_LOG_PATH, OVPMON_OPENVPN_MONITOR_CHECK_INTERVAL
+# LOGGING: OVPMON_LOGGING_LEVEL, OVPMON_LOGGING_LOG_FILE
+# RETENTION: OVPMON_RETENTION_RAW_RETENTION_DAYS, OVPMON_RETENTION_AGG_5M_RETENTION_DAYS, etc.
 FROM python:3.12-alpine
 
 WORKDIR /app
@@ -6,11 +12,12 @@ WORKDIR /app
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
-# Copy source code
+# Copy application
 COPY . .
 
-# Expose the port
+# Ensure DB directory exists
+RUN mkdir -p /app/db
+
 EXPOSE 5001
 
-# Run the API
 CMD ["python", "openvpn_api_v3.py"]