Work Item: Move app preferences and theme controls into dedicated Settings window

[ksamaschke]

Deliverable

Make the dedicated Settings window the single owner of app preferences and theme configuration, removing those concerns from the main-window information architecture.

## Dependencies
- Parent story: #203.

• Builds on existing settings-window plumbing from Work Item: Desktop foundation and startup shell plumbing (infrastructure) #207.

• No external blocker.

  Completion evidence

  • Updated preference ownership notes and settings-section map.

• Screens or descriptions showing theme and app preferences in the Settings window.

• Linked TDD items for tests and implementation.

  Acceptance criteria

  • Settings are no longer represented as a main-window tab.

• Theme controls and app preferences live in the dedicated Settings window.

• Preference ownership is separated from operational workspace content.

  Parent: Story: Dedicated settings window and app preferences #203