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/NetworkCityCore/LayoutSolver.swift

@@ -0,0 +1,40 @@
+import Foundation
+import CoreGraphics
+
+/// Places district labels so their boxes don't overlap. Each district starts at
+/// a hash-derived seed; if its (padded) label box collides with an already-placed
+/// one, we spiral outward — rotating and pushing away from downtown — until we
+/// find clear space. Existing placements never move, so the map stays stable as
+/// new districts appear.
+///
+/// Pure and deterministic given its inputs; no SpriteKit, fully unit-testable.
+public enum LayoutSolver {
+
+    /// - Parameters:
+    ///   - baseAngle/baseRadius: the hash-derived seed in polar coords.
+    ///   - localRect: the label box *relative to the node center* (labels sit
+    ///     below the dot, so this is usually offset downward).
+    ///   - existing: already-placed label boxes in world space.
+    ///   - pad: minimum gap to keep between boxes.
+    /// - Returns: a world-space center for the new district.
+    public static func placeNonOverlapping(
+        baseAngle: Double,
+        baseRadius: Double,
+        localRect: CGRect,
+        existing: [CGRect],
+        pad: CGFloat = 16,
+        maxAttempts: Int = 400
+    ) -> CGPoint {
+        for attempt in 0..<maxAttempts {
+            let angle = baseAngle + Double(attempt) * 0.45      // rotate as we go
+            let radius = baseRadius + Double(attempt) * 7       // and push outward
+            let center = CGPoint(x: cos(angle) * radius, y: sin(angle) * radius)
+            let box = localRect.offsetBy(dx: center.x, dy: center.y).insetBy(dx: -pad, dy: -pad)
+            if !existing.contains(where: { $0.intersects(box) }) {
+                return center
+            }
+        }
+        // Give up gracefully at the seed (extremely crowded map).
+        return CGPoint(x: cos(baseAngle) * baseRadius, y: sin(baseAngle) * baseRadius)
+    }
+}