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>

Tests/NetworkCityCoreTests/TrafficClassTests.swift

@@ -0,0 +1,34 @@
+import XCTest
+@testable import NetworkCityCore
+
+final class TrafficClassTests: XCTestCase {
+
+    func testQuicByProtocol() {
+        XCTAssertEqual(TrafficClass.classify(proto: .quic4, port: 443), .quic)
+        XCTAssertEqual(TrafficClass.classify(proto: .quic6, port: 12345), .quic)
+    }
+
+    func testHTTPSOverTCP() {
+        XCTAssertEqual(TrafficClass.classify(proto: .tcp4, port: 443), .https)
+    }
+
+    func testUDP443IsQuic() {
+        XCTAssertEqual(TrafficClass.classify(proto: .udp4, port: 443), .quic)
+    }
+
+    func testDNS() {
+        XCTAssertEqual(TrafficClass.classify(proto: .udp4, port: 53), .dns)
+        XCTAssertEqual(TrafficClass.classify(proto: .udp6, port: 5353), .dns)
+        XCTAssertEqual(TrafficClass.classify(proto: .tcp4, port: 53), .dns)
+    }
+
+    func testHTTP() {
+        XCTAssertEqual(TrafficClass.classify(proto: .tcp4, port: 80), .http)
+        XCTAssertEqual(TrafficClass.classify(proto: .tcp4, port: 8080), .http)
+    }
+
+    func testOther() {
+        XCTAssertEqual(TrafficClass.classify(proto: .tcp4, port: 22), .other)
+        XCTAssertEqual(TrafficClass.classify(proto: .tcp4, port: nil), .other)
+    }
+}