fix(datagrid): restore sort chevron via SF Symbols

[datlechin]

Summary

Hotfix for a regression introduced by #945. Sort chevrons stopped rendering after switching from NSImageView overlays to direct cell drawing.

The private AppKit images NSAscendingSortIndicator / NSDescendingSortIndicator only render via NSImageView (with contentTintColor) or AppKit's internal NSTableHeaderCell.drawSortIndicator. They do not produce pixels when drawn via raw NSImage.draw(in:from:operation:...) in a cell's graphics context. PR #945's drawInterior reserved layout space for the indicator (which is why column titles got truncated when sorted) but the chevron itself never appeared.

PR #942's commit history shows the previous author hit this exact issue and worked around it with overlays. #945 unknowingly reintroduced the regression.

Fix

Replace the private images with SF Symbols (chevron.up / chevron.down) configured with palette tint .secondaryLabelColor. SF Symbols draw reliably via image.draw(in:) and the palette config handles tinting in both Light and Dark modes.

private static func indicatorImage(for direction: SortDirection) -> NSImage? {
    let symbolName = direction == .ascending ? "chevron.up" : "chevron.down"
    let config = NSImage.SymbolConfiguration(pointSize: priorityFontSize, weight: .semibold)
        .applying(.init(paletteColors: [.secondaryLabelColor]))
    return NSImage(systemSymbolName: symbolName, accessibilityDescription: nil)?
        .withSymbolConfiguration(config)
}

One file changed, 5 insertions / 6 deletions.

Test plan

• Click a column header to sort: chevron appears next to title
• Shift-click a second column: both columns show chevrons (primary alone, secondary with priority number "2")
• Click sorted descending column third time: chevron disappears (sort cleared)
• Toggle Light / Dark mode: chevron tints to secondaryLabelColor correctly in both
• `xcodebuild build` — clean
• `swiftlint lint --strict` — 0 violations