refactor(apple): decompose ContentView (735 -> 272 lines)

Split the monolithic ContentView into focused view files — a pure structural refactor
with no behavior change (verified: builds macOS/iOS/tvOS, the test suite is green, and a
fidelity review against the original found no discrepancies):

- ContentView (272): the coordinator — owns the session model / host store / discovery,
  switches home<->session, holds the connect logic (it reads @AppStorage) + the dev
  hooks, and the stream builder (whose stable identity across awaiting-trust->streaming
  must NOT move — it stays here).
- HomeView (251): the hosts grid + navigation + toolbar + sheets + "On this network"
  discovery section + empty state.
- HostCards (158): HostCardView + DiscoveredCardView, sharing a CardMetrics struct
  (dedupes the platform-tuned sizing the two cards had copy-pasted).
- TrustCardView (80): the TOFU prompt + fingerprint formatting.
- StreamHUDView (67): the streaming overlay HUD.

State flows idiomatically: @StateObject (ContentView) -> @ObservedObject in subviews,
@State -> @Binding; the connect logic is passed as closures. Sheet placement is
preserved — the pairing/speed-test sheets stay on the outer body so they survive the
trust->home transition.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/StreamHUDView.swift

@@ -0,0 +1,67 @@
+// The streaming overlay HUD: mode + fps/throughput, the capture→client (and, under the stage-2
+// presenter, capture→present) latency lines, the platform input hint, and disconnect.
+
+import PunktfunkKit
+import SwiftUI
+
+struct StreamHUDView: View {
+    @ObservedObject var model: SessionModel
+    let connection: PunktfunkConnection
+
+    var body: some View {
+        VStack(alignment: .trailing, spacing: 4) {
+            HStack(spacing: 6) {
+                Circle()
+                    .fill(Color.accentColor)
+                    .frame(width: 7, height: 7)
+                Text("\(connection.width)×\(connection.height)@\(connection.refreshHz)  \(model.fps) fps  \(model.mbps, specifier: "%.1f") Mb/s")
+                    .font(.system(.caption, design: .monospaced))
+            }
+            if model.latencyValid {
+                // Capture→client-receipt (skew-corrected); excludes the layer's decode+present —
+                // see LatencyMeter. "(same-host)" when the host didn't answer the skew handshake.
+                Text("capture→client \(model.latencyP50Ms, specifier: "%.1f")/\(model.latencyP95Ms, specifier: "%.1f") ms p50/p95\(model.latencySkewCorrected ? "" : " (same-host)")")
+                    .font(.system(.caption2, design: .monospaced))
+                    .foregroundStyle(.secondary)
+            }
+            if model.presentLatencyValid {
+                // Capture→present (glass-to-glass, modulo host render→capture) — stage-2 presenter
+                // only; stage-1's layer presents internally with no per-frame stamp.
+                Text("capture→present \(model.presentLatencyP50Ms, specifier: "%.1f")/\(model.presentLatencyP95Ms, specifier: "%.1f") ms p50/p95\(model.presentLatencySkewCorrected ? "" : " (same-host)")")
+                    .font(.system(.caption2, design: .monospaced))
+                    .foregroundStyle(.secondary)
+            }
+            // While captured the cursor is hidden+frozen, so the button is keyboard-only
+            // (⌘⎋ or Cmd+Tab release the cursor; released, it's clickable again).
+            #if os(macOS)
+            Text(model.mouseCaptured
+                ? "⌘⎋ releases the mouse"
+                : "Click the stream to capture input")
+                .font(.caption2)
+                .foregroundStyle(.secondary)
+            #elseif os(iOS)
+            // Touch always plays directly; ⌘⎋ (hardware keyboard) toggles kb/mouse.
+            Text(model.mouseCaptured
+                ? "⌘⎋ releases keyboard & mouse"
+                : "⌘⎋ captures keyboard & mouse")
+                .font(.caption2)
+                .foregroundStyle(.secondary)
+            #endif
+            #if os(tvOS)
+            // No focusable control during play: a focusable button steals the controller's
+            // A press (the focus engine consumes it before the host sees it). Disconnect is
+            // the Siri Remote's Menu button (.onExitCommand on the stream) — just hint it.
+            Text("Press Menu to disconnect")
+                .font(.caption)
+                .foregroundStyle(.secondary)
+            #else
+            Button("Disconnect (⌘D)") { model.disconnect() }
+                .font(.caption)
+                .keyboardShortcut("d", modifiers: .command)
+            #endif
+        }
+        .padding(10)
+        .background(.regularMaterial, in: RoundedRectangle(cornerRadius: 10))
+        .padding(10)
+    }
+}