feat(design): graphic design help for the web console #137

Summary

Help wanted: graphic design for the Fleet Manager web console. The console was built feature by feature, and it needs a consistent visual layer before v0.1.0. A dedicated design pass is planned right before the v0.1.0 tag. Outside contributions are welcome before then, and will feed into it.

What's needed:

• Visual design: a cohesive look across pages, with spacing, colour and type that work in light and dark themes.
• Iconography: one consistent icon set for navigation, node roles (root, intermediate, issuing), certificate states (valid, revoked, expired) and actions.
• Empty-state and illustration images: for lists with no data yet (no nodes, no certificates, no agent keys, no approvals) and first-run screens.
• Favicon and logo usage: favicon sizes, the app mark in the header, and clear-space and colour rules for the logo.
• Screenshots: a clean, repeatable set of console screenshots, using documentation values only (for example fleetos.example.org and Example Root CA G1), for the README and the docs.

Acceptance criteria

• Assets are delivered as SVG (preferred) or PNG at 1x and 2x where SVG doesn't fit, optimised and without embedded fonts or tracking metadata.
• Assets live under public/ (favicon, logo) and src/assets/ (icons, illustrations), with a short src/assets/README.md listing each file and its use.
• Colours map onto the existing design tokens in src/index.css. Any new token is documented there.
• Every contribution is licensed under this repository's Apache-2.0 licence, with a DCO sign-off on each commit (see CONTRIBUTING).
• Screenshots contain no real hostnames, addresses, names or keys.

Tasks

• Icon set and navigation icons
• Empty-state illustrations
• Favicon and logo usage
• Console screenshot set

Notes

• Related: feat(web): run the CryptOS web UI through a design review #110 (design review of the existing screens).
• The docs site has a matching request for diagrams and images: CryptOS-PKI/docs, "graphic design help for the documentation site".