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/KeyboardHint.swift

@@ -0,0 +1,19 @@
+import SwiftUI
+
+struct KeyboardHint: View {
+    let title: String
+
+    var body: some View {
+        Text(title)
+            .font(.caption2.weight(.semibold))
+            .monospaced()
+            .foregroundStyle(.secondary)
+            .padding(.horizontal, 6)
+            .padding(.vertical, 4)
+            .background(.regularMaterial, in: RoundedRectangle(cornerRadius: 6, style: .continuous))
+            .overlay(
+                RoundedRectangle(cornerRadius: 6, style: .continuous)
+                    .strokeBorder(Color.primary.opacity(0.08), lineWidth: 1)
+            )
+    }
+}