Make keyboard focus states clearer in the desktop app

[Muawiya-contact]

Goal

Make keyboard focus in the desktop app easier to see.

Right now the app has buttons and collapsible sections, but keyboard users should get a clear visible focus ring when tabbing through actions.

Why this helps

This is a small UI polish issue that improves accessibility and makes the app feel more professional.

Suggested starting point

Look in:

app/src/styles.css

A simple first version could add a shared focus style:

button:focus-visible {
  outline: 2px solid #3498db;
  outline-offset: 3px;
}

Please test the main actions:

• Choose folder
• Cancel scan
• Expand/collapse result sections
• Quarantine / restore / purge buttons

Acceptance criteria

• Keyboard focus is clearly visible.
• Mouse users do not see a focus ring on normal clicks.
• Existing app frontend tests still pass.