Initial commit: NetworkCity — network traffic as a neon city

A native macOS network monitor that renders live traffic as a top-down
neon city: your Mac is downtown, remote orgs are glowing districts, and
traffic is cars of light driving the roads.

Architecture:
- NetworkCityCore: swappable data layer behind a ConnectionSource protocol
  (nettop-backed today), plus pure/tested logic — traffic diffing, org
  classification (reverse-DNS + CIDR), traffic classes, hub-and-spoke
  expansion policy, label anti-overlap, and latency→distance layout.
- NetworkCityApp: SwiftUI + SpriteKit city — auto-expanding districts,
  protocol-coloured cars, click-to-inspect panel, and latency-as-distance
  (districts glide to their measured RTT).
- nettop-probe: CLI proof of the data layer.

44 tests passing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Sources/NetworkCityApp/NetworkCityApp.swift

@@ -0,0 +1,27 @@
+import SwiftUI
+import AppKit
+
+@main
+struct NetworkCityApp: App {
+    @NSApplicationDelegateAdaptor(AppDelegate.self) private var delegate
+    @StateObject private var controller = TrafficController()
+
+    var body: some Scene {
+        WindowGroup("NetworkCity") {
+            CityView(controller: controller)
+                .frame(minWidth: 900, minHeight: 620)
+                .background(.black)
+        }
+        .windowStyle(.hiddenTitleBar)
+    }
+}
+
+/// Running as an SPM executable (no app bundle), so promote ourselves to a
+/// regular foreground app and grab focus on launch.
+final class AppDelegate: NSObject, NSApplicationDelegate {
+    func applicationDidFinishLaunching(_ notification: Notification) {
+        NSApp.setActivationPolicy(.regular)
+        NSApp.activate(ignoringOtherApps: true)
+    }
+    func applicationShouldTerminateAfterLastWindowClosed(_ app: NSApplication) -> Bool { true }
+}