UI: add Playwright screenshots for discovery import and merged network views

[BadgerOps]

Follow-up to #187 and PR #188.

Summary

Add screenshot coverage for the new discovery import and merged network UI flows.

Why

PR #188 added substantial UI surface. Screenshots will make visual regressions easier to catch and provide before/after artifacts for review.

Scope

• Add or extend Playwright screenshot scripts for the Discovery page.
• Capture checkbox multi-select import preview.
• Capture merged hierarchy view.
• Capture flat network view.
• Capture conflict review panel or current conflict list.
• Save outputs under photos/ following existing repo conventions.

Acceptance Criteria

• Screenshot generation runs against a local app URL.
• Generated screenshots cover desktop and at least one narrow/mobile viewport where practical.
• PR documentation explains how to regenerate the screenshots.