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/GlassChrome.swift

@@ -0,0 +1,23 @@
+import SwiftUI
+
+public extension View {
+    @ViewBuilder
+    func sioGlassChrome() -> some View {
+        if #available(iOS 26.0, macOS 26.0, *) {
+            self.glassEffect(.regular)
+        } else {
+            self.background(.regularMaterial)
+        }
+    }
+
+    @ViewBuilder
+    func sioGlassSurface<S: Shape>(in shape: S, tint: Color? = nil) -> some View {
+        if #available(iOS 26.0, macOS 26.0, *) {
+            self.glassEffect(Glass.regular.tint(tint), in: shape)
+        } else {
+            self.background(.regularMaterial, in: shape)
+                .overlay(shape.stroke(Color.primary.opacity(0.08), lineWidth: 1))
+                .overlay(shape.fill((tint ?? .clear).opacity(0.08)))
+        }
+    }
+}