refactor(datagrid): cleanup

[datlechin]

Summary

DataGrid Phase 4 — full cleanup refactor addressing 8 verified audit items in 1 atomic PR.

Real bugs (5)

• Fix appcast.xml to support both ARM64 and x86_64 via universal binary #43 — headerFont was a computed property recreating NSFont on every call. Now private static let.
• fix: support macOS 13.5+ (Ventura) — downgrade all macOS 14+ APIs #41 — Theme observer Task missing @MainActor. Added annotation.
• feat: add Show Structure to sidebar context menu #38 — sanitizedForCellDisplay did double scan (containsLineBreak then replacement). Now true single-pass.
• Add Sparkle auto-update integration #42 — Column reorder O(n²) (firstIndex(where:) per slot). Built [NSUserInterfaceItemIdentifier: Int] index map, O(1) lookup.
• feat: improve filter panel UI/UX #37 — removeChangeAt O(N) per removal (loop updating changeIndex dict). Replaced with swap-and-pop, O(1).

Quality (3)

• Add multi-line text editor for long text fields #22 — Removed pendingDropdown* instance vars from coordinator. Use NSMenuItem.representedObject carrying DropdownMenuContext reference type instead.
• Add Intel Mac support with separate build strategy #18 — Routed remaining inline column - 1 / column >= 1 boundary checks through centralized helpers firstDataTableColumnIndex + isDataTableColumn(_:). Migrated KeyHandlingTableView + DataGridView+Editing.
• [ImgBot] Optimize images #53 — Consolidated mixed displayCache.removeAll() + rebuildVisualStateCache() callsites into single invalidateAllDisplayCaches() method. Format-only and teardown invalidations kept narrower (different scope).

Files

8 files modified, +121 / -67:

• TablePro/Core/ChangeTracking/PendingChanges.swift
• TablePro/Views/Results/DataGridCellFactory.swift
• TablePro/Views/Results/DataGridColumnPool.swift
• TablePro/Views/Results/DataGridCoordinator.swift
• TablePro/Views/Results/DataGridView.swift
• TablePro/Views/Results/Extensions/DataGridView+Editing.swift
• TablePro/Views/Results/Extensions/DataGridView+Popovers.swift
• TablePro/Views/Results/KeyHandlingTableView.swift

Test plan

• xcodebuild build (compile check)
• swiftlint lint --strict
• Manual: open table, verify header rendering unchanged
• Manual: dropdown cell click → popover opens with correct row/col context
• Manual: column reorder by drag persists correctly
• Manual: cell with line breaks renders single-line correctly
• Manual: theme switch updates fonts without crash
• Manual: undo cell edit / row delete works (changeIndex correctness)
• Manual: keyboard arrow nav across columns (boundary helpers)