Implement a Zed-inspired design in the fork #3

Part of #2. First establish the appearance we want by implementing it directly in this fork. Hardcoded styling is acceptable in this stage; generalizing it is the next sub-issue.

Scope:

• Choose concrete Zed references and define which parts of the appearance to adopt before changing the UI.
• Apply the agreed colors, typography, spacing, shapes, icons, and layout changes where needed.
• Verify the affected web and desktop flows, including light/dark appearance, narrow windows, and remote connections where applicable. Decide explicitly which changes apply to mobile.
• Capture before/after images and a short recording for changed motion or timing.

Acceptance:

• The implemented screens match the agreed references and remain usable.
• Visual evidence identifies the final design that the follow-up will make configurable.
• The styling introduces no continuously repainting animations or loss of keyboard access.

This issue does not add a generic customization system. The following sub-issue audits the final changes and makes them reusable.