Fix label overlap when districts glide to their latency distance

The latency reposition moved hubs to their RTT radius without checking
label collisions, so a gliding district could land on top of a neighbour.
Make both placement paths overlap-aware via the existing LayoutSolver:
keep distance = latency (the meaningful axis) but rotate the arbitrary
angle to clear other labels. Track each hub's target position so
same-tick moves avoid where others are heading, not just where they are.

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

Sources/NetworkCityApp/CityScene.swift

@@ -38,6 +38,7 @@ final class CityScene: SKScene {
     private var buildings: [String: BuildingNode] = [:]
     private var roads: [String: SKShapeNode] = [:]
     private var latencyRadius: [String: CGFloat] = [:]
+    private var targetPos: [String: CGPoint] = [:]   // where each hub is heading
     private var ringKey: String?
     private let roadLayer = SKNode()
     private let carLayer = SKNode()
@@ -234,6 +235,7 @@ final class CityScene: SKScene {
 
         let node = BuildingNode(title: title, subtitle: subtitle)
         node.position = placement(for: key, footprint: node.labelFootprint)
+        targetPos[key] = node.position
         node.alpha = 0
         node.run(.fadeIn(withDuration: 0.6))
         buildingLayer.addChild(node)
@@ -266,8 +268,19 @@ final class CityScene: SKScene {
         if let current = latencyRadius[key], abs(current - target) < 18 { return }
         latencyRadius[key] = target
 
+        // Keep distance = latency, but rotate/nudge the (arbitrary) angle to
+        // clear other labels — otherwise gliding hubs land on top of each other.
         let angle = atan2(building.position.y, building.position.x)
-        let dest = CGPoint(x: cos(angle) * Double(target), y: sin(angle) * Double(target))
+        let others = buildings.compactMap { (k, b) -> CGRect? in
+            guard k != key else { return nil }
+            let p = targetPos[k] ?? b.position
+            return b.labelFootprint.offsetBy(dx: p.x, dy: p.y)
+        }
+        let dest = LayoutSolver.placeNonOverlapping(
+            baseAngle: angle, baseRadius: Double(target),
+            localRect: building.labelFootprint, existing: others, pad: 18
+        )
+        targetPos[key] = dest
         building.run(.move(to: dest, duration: 0.8))
 
         if let road = roads[key] {
@@ -287,8 +300,9 @@ final class CityScene: SKScene {
         let ring = Double((h >> 16) % 1000) / 1000
         let baseRadius = 165 + Double(ring) * Double(worldRadius - 165)
 
-        let existing = buildings.values.map {
-            $0.labelFootprint.offsetBy(dx: $0.position.x, dy: $0.position.y)
+        let existing = buildings.map { (k, b) in
+            let p = targetPos[k] ?? b.position
+            return b.labelFootprint.offsetBy(dx: p.x, dy: p.y)
         }
         return LayoutSolver.placeNonOverlapping(
             baseAngle: baseAngle, baseRadius: baseRadius,