Add NSTableView/NSOutlineView cell reuse to AppKit views

[2witstudios]

Problem

Two AppKit view controllers create brand new cell views on every reload instead of using the standard makeView(withIdentifier:owner:) cell reuse pattern:

SidebarOutlineViewController (710 lines)

• makeProjectCell, makeWorktreeCell, makeAgentCell (lines 272-397) create fresh NSTableCellView + NSStackView instances every time outlineView(_:viewFor:item:) is called
• rebuildNodes is called from updateNSViewController which fires on every SwiftUI state change, creating allocation pressure

CommandPaletteViewController (~640 lines)

• tableView(_:viewFor:row:) (lines 667-717) creates new cells every call
• filterVariants calls reloadData() on every keystroke, so typing creates new views for every filtered result on every character

Impact

Without cell reuse:

• Scrolling or frequent reloads allocate and discard many views
• GC pressure increases with more items
• Performance degrades with larger lists

Suggested approach

1. Register cell identifiers for each cell type
2. Use makeView(withIdentifier:owner:) to reuse cells
3. Configure the reused cell's content instead of rebuilding the view hierarchy

Files

• apps/purepoint-macos/purepoint-macos/Views/Sidebar/SidebarOutlineViewController.swift
• apps/purepoint-macos/purepoint-macos/Views/CommandPalette/CommandPalettePanel.swift