feat: logging system and reduced logs

docs/LOGGING.md

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+# SPORE UI Backend Logging
+
+The SPORE UI backend now includes a configurable logging system to reduce log noise while maintaining important information.
+
+## Log Levels
+
+The logging system supports different levels:
+
+- **INFO**: Important operational messages (default)
+- **DEBUG**: Detailed debugging information (only shown when enabled)
+- **WARN**: Warning messages
+- **ERROR**: Error messages
+
+## Controlling Log Levels
+
+### Environment Variables
+
+Set the `LOG_LEVEL` environment variable to control logging:
+
+```bash
+# Show only INFO, WARN, and ERROR messages (default)
+LOG_LEVEL=info
+
+# Show all messages including DEBUG
+LOG_LEVEL=debug
+```
+
+### Development Mode
+
+In development mode (`NODE_ENV=development`), DEBUG messages are automatically enabled:
+
+```bash
+NODE_ENV=development npm start
+```
+
+## What Was Changed
+
+The following verbose logging has been moved to DEBUG level:
+
+1. **Heartbeat Messages**: Regular heartbeat logs from nodes
+2. **WebSocket Broadcasts**: Routine cluster update broadcasts
+3. **Proxy Calls**: Individual API proxy request details
+4. **Cluster Updates**: Member list change notifications
+5. **Discovery Events**: Routine node discovery messages
+
+## Important Messages Still Shown
+
+These messages remain at INFO level for operational visibility:
+
+- Node discovery (new nodes)
+- Node status changes (inactive/stale)
+- Failover events
+- Server startup/shutdown
+- Error conditions
+
+## Example Usage
+
+```bash
+# Production with minimal logging
+LOG_LEVEL=info npm start
+
+# Development with full debugging
+LOG_LEVEL=debug npm start
+
+# Or use development mode
+NODE_ENV=development npm start
+```
+
+This reduces log noise significantly while preserving important operational information.