Add explicit accessible names to settings sliders

[ajhcs]

Associate each WPF settings slider with an accessible name that includes its visible label and exposes the current value without changing the visual layout.

Acceptance criteria

• Windows Narrator announces the purpose and current value of every slider.
• Existing keyboard behavior and visual layout remain unchanged.
• The contribution documents the Windows and Narrator versions used for manual verification.
• Existing visual regression checks continue to pass.

Helpful starting point

Most settings controls are assembled in src/CodexEdgeGlow/SettingsWindow.cs.