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/Sources/Core/Design/AvatarView.swift

@@ -0,0 +1,21 @@
+import SwiftUI
+
+struct AvatarView: View {
+    let name: String
+    var color: Color = SIO.tint
+    var size: CGFloat = 30
+
+    var body: some View {
+        Text(initials)
+            .font(.system(size: size * 0.42, weight: .semibold, design: .rounded))
+            .foregroundStyle(.white)
+            .frame(width: size, height: size)
+            .background(color, in: Circle())
+            .overlay(Circle().strokeBorder(.white.opacity(0.16), lineWidth: 1))
+    }
+
+    private var initials: String {
+        let parts = name.split(separator: " ")
+        return String(parts.prefix(2).compactMap { $0.first }).uppercased()
+    }
+}