Add theme picker preview window

[cyanzhong]

No description provided.

[Copilot]

🟡 Changes recommended

The unresolved main-actor isolation issue can prevent the warnings-as-errors build from compiling.

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Pull request overview

Adds floating previews for built-in themes in the editor settings menus when hovered.

Changes:

• Adds palette data for built-in themes.
• Introduces reusable preview panels.
• Tracks native menu highlighting and positions previews.

Blocking critical finding: ThemeMenuPreview requires @MainActor isolation, or its controller initialization must move into an isolated initializer, to avoid strict-concurrency build failures.

File summaries

File	Summary
MarkEditMac/Sources/Settings/EditorSettingsView.swift	Integrates menu tracking and preview positioning.
MarkEditMac/Sources/Main/AppTheme.swift	Defines preview palettes for built-in themes.
MarkEditMac/Modules/Sources/SharedUI/ThemePreview.swift	Provides configurable floating preview panels.
MarkEditMac/Modules/Sources/SharedUI/MenuHighlightTracker.swift	Reports highlighted native menu items.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🔵 Needs a closer look

Theme preview positioning has an unresolved coordinate-system issue.

Review details

Suppressed comments (1)

MarkEditMac/Sources/Settings/EditorSettingsView.swift:250

• accessibilityFrame() uses the accessibility screen coordinate system, whose y-axis is top-down, while NSScreen.frame/visibleFrame and NSWindow.setFrameOrigin use AppKit's bottom-up screen coordinates. Passing this rect through unchanged makes the preview appear at the wrong vertical position (and can choose the wrong display on multi-monitor setups); convert the frame before both the screen lookup and placement.

        rowFrame: item?.accessibilityFrame()

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🔵 Needs a closer look

One or more issues must be addressed before approval.

Review details

Suppressed comments (1)

MarkEditMac/Modules/Sources/SharedUI/ThemePreview.swift:70

• After rootView is replaced, fittingSize is read without forcing the hosting view to lay out. Since the panel is initially built with an empty preview, this can leave the first preview at a stale or zero size; the existing View.measuredSize helper explicitly calls needsLayout and layoutSubtreeIfNeeded() before reading fittingSize (MarkEditMac/Modules/Sources/TextCompletion/Extensions/View+Extension.swift:11-15). Flush the hosting view's layout before sizing the panel.

    panel.setContentSize(previewView.fittingSize)

• Files reviewed: 5/5 changed files
• Comments generated: 0 new
• Review effort level: Lite