Restructure documentation into separate files with links

docs/TROUBLESHOOTING.md

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+# Troubleshooting Guide
+
+## Port Already in Use
+
+If port 3001 is already in use, change it in `.env`:
+```env
+PORT=3002
+```
+
+Then restart the server.
+
+## Email Not Sending
+
+- Verify SMTP credentials are correct
+- Check that 2FA is enabled and you're using an app password (for Gmail)
+- Test with a simple SMTP client first
+- Check server logs for specific error messages
+- Verify EMAIL_ENABLED=true in .env
+- Ensure EMAIL_TO is set to a valid email address
+
+## Resource Not Being Checked
+
+- Verify resource is enabled (toggle in dashboard)
+- Check server logs for errors with `pm2 logs resource-monitor`
+- Ensure URL is accessible from the server (try `curl https://url` from server)
+- Verify the resource type matches (http, https, ping, etc.)
+- Check that the check interval is set to a reasonable value
+
+## White Screen on Load
+
+- Hard refresh browser (Ctrl+Shift+R on Windows, Cmd+Shift+R on Mac)
+- Clear browser cache
+- Check console for JavaScript errors (F12 → Console)
+- Verify build files are in `client/build/` directory
+- Make sure you committed build files before deploying
+
+## History Page Slow
+
+- Toggle off "Show Averages" if viewing large time windows
+- Use the 7-day view instead of 30 days
+- Check server load with `pm2 monit`
+- Increase server resources if needed
+
+## Database Issues
+
+- Check that `/opt/resource-monitor/data/` directory exists and is writable
+- Verify database file permissions: `ls -la data/skywatch.db`
+- If corrupted, delete database and restart to rebuild from scratch
+
+## Memory Issues
+
+- Monitor with `pm2 monit`
+- Check cache size with GET `/api/cache/clear` endpoint
+- Reduce data retention period
+- Enable auto-cleanup in settings
+
+## Connection Refused
+
+- Verify server is running: `pm2 list`
+- Check port is correct: `netstat -an | grep 3001` (Linux) or `netstat -ano | findstr 3001` (Windows)
+- Check firewall rules allow port 3001
+- Verify .env PORT setting matches
+
+## Incidents Not Triggering
+
+- Verify consecutive_failures threshold is met (default: 3)
+- Check grace_period setting (default: 300 seconds)
+- Review alert settings in Settings page
+- Check notification service is enabled
+- View server logs: `pm2 logs resource-monitor`
+
+## API Endpoints Not Working
+
+- Verify server is running on correct port
+- Check CORS settings if accessing from different domain
+- Review request method (GET vs POST)
+- Check error response for specific error message
+- Verify request parameters are correct
+
+## Performance Issues
+
+- Use averaged mode in history (default is enabled)
+- Increase check intervals for resources
+- Enable caching (default is 2 minutes)
+- Consider archiving old data
+- Monitor database size: `ls -lh data/skywatch.db`