Adjust focus mode dimming for dark mode visibility

[Copilot]

Focus mode dims non-active paragraphs to help writers concentrate. The fixed 30% opacity made defocused text nearly invisible in dark mode.

Changes

• Detect appearance mode using NSApp.effectiveAppearance
• Apply adaptive dimming: 50% opacity in dark mode, 30% in light mode
• Modified applyFocusMode() in EditorView.swift

// Before
textStorage.addAttribute(.foregroundColor, 
    value: NSColor.labelColor.withAlphaComponent(0.3), 
    range: fullRange)

// After
let isDarkMode = appearance.bestMatch(from: [.darkAqua, .aqua]) == .darkAqua
let dimmedAlpha: CGFloat = isDarkMode ? 0.5 : 0.3
textStorage.addAttribute(.foregroundColor, 
    value: NSColor.labelColor.withAlphaComponent(dimmedAlpha), 
    range: fullRange)

The higher opacity in dark mode preserves visibility while maintaining the focus effect.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>UI/UX problem: Focus mode not fully compatible with Dark mode</issue_title>
<issue_description>Focus mode is not fully compatible with Dark Mode. Defocused sections are barely discernible.

Options:

• Disable focus mode when Dark Mode is on
• Adjust defocused content font color for Dark Mode.

---

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes UI/UX problem: Focus mode not fully compatible with Dark mode #22

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Note

Improves readability of defocused paragraphs in focus mode by adapting dimming to the system appearance.

• In EditorView.swift applyFocusMode(), detect dark/light mode via NSApp.effectiveAppearance and set dimmedAlpha to 0.5 (dark) or 0.3 (light)
• Apply NSColor.labelColor.withAlphaComponent(dimmedAlpha) to the full text, then restore full color for the current paragraph

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