M7 #3: Chat 'Connecting…' overlay during SSH exec handshake

ChatController already transitioned through a `.connecting` state
between tap-Chat and first-message-ready (ACP initialize + session/new
take ~0.5–1.5 s on a warm network), but there was no visible UI
— the screen stayed on the idle layout with a disabled composer.
Users interpreted the silence as a frozen app (pass-1 M7 #3).

Adds a `.regularMaterial` overlay with a large ProgressView +
"Connecting to <nickname>…" text, rendered whenever
`controller.state == .connecting`. Disappears automatically when
state flips to `.ready` (normal path) or `.failed` (handoff to the
existing errorOverlay).

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

scarf/Scarf iOS/Chat/ChatView.swift

@@ -63,6 +63,8 @@ struct ChatView: View {
         .overlay {
             if case .failed(let msg) = controller.state {
                 errorOverlay(msg)
+            } else if controller.state == .connecting {
+                connectingOverlay
             }
         }
         .sheet(item: Binding(
@@ -163,6 +165,24 @@ struct ChatView: View {
         .background(.regularMaterial)
     }
 
+    /// Shown while we're opening the SSH exec channel + spawning
+    /// `hermes acp` + creating the ACP session. Typically ~0.5–1.5 s
+    /// on a warm network — silent before this overlay existed, which
+    /// made the app feel frozen (pass-1 M7 #3).
+    @ViewBuilder
+    private var connectingOverlay: some View {
+        VStack(spacing: 12) {
+            ProgressView()
+                .controlSize(.large)
+            Text("Connecting to \(config.displayName)…")
+                .font(.callout)
+                .foregroundStyle(.secondary)
+        }
+        .padding(24)
+        .background(.regularMaterial)
+        .clipShape(RoundedRectangle(cornerRadius: 14))
+    }
+
     @ViewBuilder
     private func errorOverlay(_ message: String) -> some View {
         VStack(spacing: 12) {