fix(dashboard): center responsive product layout

[yiaany]

Summary

• center the complete README hero, including GhostAPI, badges, navigation links, and install command
• center the dashboard identity against the full viewport rather than the sidebar-adjusted content area
• add a mobile navigation drawer and vertical request/detail layout without horizontal overflow
• refresh the dashboard screenshot from the real local server and add layout regression coverage

Verification

• npm run lint
• npm run typecheck
• npm test (343 tests)
• npm run build
• browser geometry at 1440x900: brand center 720 / viewport center 720, body width 1440
• browser geometry at 390x844: brand center 195 / viewport center 195, body width 390, mobile drawer and vertical panes verified

[ecc-tools]

ECC bundle files are already tracked in this repository. Skipping generation of another bundle PR.

[github-actions]

GhostAPI PR safety

Result: success

The status check and sanitized evidence artifact are the source of truth. This comment is updated in place and contains no request traffic or secrets.