WIP: local handoff implementation

Local work on the social.io handoff before merging the claude
worktree branch. Includes the full per-spec Sources/Core/Design
module (8 files), watchOS target under WatchApp/, Live Activity +
widget extension, entitlements, scheme, and asset catalog.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

swift/WatchApp/Design/SIOTokens.swift

@@ -0,0 +1,32 @@
+import SwiftUI
+
+enum SIO {
+    static let tint = Color(red: 0.184, green: 0.420, blue: 1.0)
+    static let laneFeed = Color(red: 0.184, green: 0.420, blue: 1.0)
+    static let lanePaper = Color(red: 1.0, green: 0.624, blue: 0.039)
+    static let lanePeople = Color(red: 0.188, green: 0.819, blue: 0.345)
+}
+
+enum Lane: String, CaseIterable, Codable, Identifiable {
+    case feed
+    case paper
+    case people
+
+    var id: String { rawValue }
+
+    var label: String {
+        switch self {
+        case .feed: "Feed"
+        case .paper: "Paper"
+        case .people: "People"
+        }
+    }
+
+    var color: Color {
+        switch self {
+        case .feed: SIO.laneFeed
+        case .paper: SIO.lanePaper
+        case .people: SIO.lanePeople
+        }
+    }
+}