initial commit: Proximity iOS app proposal, full Swift code scaffold, reference backend, testing docs, generated Xcode project

Proximity/Models/DistanceTier.swift

@@ -0,0 +1,49 @@
+import Foundation
+
+/// The physical range band a user is open to connecting within.
+///
+/// Each tier maps to a different sensing technology. The tiers are ordered so
+/// higher tiers *include* lower ones (being open "in the area" also means
+/// you're open "nearby" and "right here").
+enum DistanceTier: Int, CaseIterable, Identifiable, Codable {
+    /// 0–9 m. Ultra-wideband (Nearby Interaction). "This exact person."
+    case rightHere = 1
+
+    /// 10–100 m. Bluetooth Low Energy / iBeacon. "This room, this block."
+    case nearby = 2
+
+    /// 100 m–50 mi. Server-relayed, opt-in coarse location. "This neighborhood."
+    case inTheArea = 3
+
+    var id: Int { rawValue }
+
+    var title: String {
+        switch self {
+        case .rightHere: return "Right Here"
+        case .nearby:    return "Nearby"
+        case .inTheArea: return "In the Area"
+        }
+    }
+
+    var subtitle: String {
+        switch self {
+        case .rightHere: return "0–9 m · UWB"
+        case .nearby:    return "10–100 m · BLE"
+        case .inTheArea: return "100 m–50 mi · Network"
+        }
+    }
+
+    /// The primary engine used for this tier.
+    var engine: ProximityEngine {
+        switch self {
+        case .rightHere: return .uwb
+        case .nearby:    return .ble
+        case .inTheArea: return .beacon
+        }
+    }
+
+    /// Higher tiers include lower ones.
+    func includes(_ other: DistanceTier) -> Bool {
+        self.rawValue >= other.rawValue
+    }
+}