Add anonymized interface previews

[dude2k]

Summary

• add an interface preview section to the README
• include dashboard, task, and result screenshots captured from the real portal
• use synthetic task names and RFC 5737 documentation addresses so no private infrastructure is exposed
• make each preview clickable at full resolution and provide descriptive alternative text

Impact

Prospective users can understand the portal layout and core workflows before deploying MultiSpeed.

Verification

• visually inspected all three screenshots
• confirmed visible IP addresses use 192.0.2.10
• ran the deterministic operator workflow and screenshot capture: 2 Playwright tests passed
• git diff --check