feat(resize/apple): resize overlay — blur + spinner during mid-stream resize

Make a Match-window resize deliberate instead of a stutter: blur the live
stream and show a spinner while the host rebuilds its virtual display +
encoder and VideoToolbox re-inits on the new-mode IDR. No new protocol —
driven entirely by existing client signals.

- ResizeIndicator (pure core, unit-tested): START = follower steering,
  END = a decoded frame at the target size, TIMEOUT = 2.5s safety net for a
  rejected/capped switch that never yields a new-size frame; re-arms only on
  a CHANGED target, not a repeated same-size drag.
- MatchWindowFollower.onResizeTarget fires the instant the window differs
  from the live mode (deduped via lastSteered); a new onDecodedSize callback
  threads each new-mode IDR's coded dims through StreamPump/Stage2Pipeline →
  SessionPresenter → both stream views.
- SessionModel gains @Published resizing (+ resizeTargeted/resizeDecoded, a
  tick on the 1 Hz stats timer, reset on disconnect); ContentView blurs the
  stream 16px and overlays ResizeIndicatorView while resizing (the 32px
  trust-prompt blur is unchanged and takes precedence).

tvOS declares the props but never fires the follower (it drives modes via
AVDisplayManager), so the overlay stays dormant there. Pure core verified on
the Linux toolchain; full AppKit/UIKit build pending on a Mac.

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

clients/apple/Sources/PunktfunkKit/Views/StreamView.swift

@@ -87,6 +87,8 @@ public struct StreamView: NSViewRepresentable {
     private let onDisconnectRequest: (() -> Void)?
     private let onFrame: (@Sendable (AccessUnit) -> Void)?
     private let onSessionEnd: (@Sendable () -> Void)?
+    private let onResizeTarget: ((UInt32, UInt32) -> Void)?
+    private let onDecodedSize: (@Sendable (Int, Int) -> Void)?
     private let endToEndMeter: LatencyMeter?
     private let decodeMeter: LatencyMeter?
     private let displayMeter: LatencyMeter?
@@ -108,6 +110,8 @@ public struct StreamView: NSViewRepresentable {
         onDisconnectRequest: (() -> Void)? = nil,
         onFrame: (@Sendable (AccessUnit) -> Void)? = nil,
         onSessionEnd: (@Sendable () -> Void)? = nil,
+        onResizeTarget: ((UInt32, UInt32) -> Void)? = nil,
+        onDecodedSize: (@Sendable (Int, Int) -> Void)? = nil,
         endToEndMeter: LatencyMeter? = nil,
         decodeMeter: LatencyMeter? = nil,
         displayMeter: LatencyMeter? = nil
@@ -118,6 +122,8 @@ public struct StreamView: NSViewRepresentable {
         self.onDisconnectRequest = onDisconnectRequest
         self.onFrame = onFrame
         self.onSessionEnd = onSessionEnd
+        self.onResizeTarget = onResizeTarget
+        self.onDecodedSize = onDecodedSize
         self.endToEndMeter = endToEndMeter
         self.decodeMeter = decodeMeter
         self.displayMeter = displayMeter
@@ -131,6 +137,8 @@ public struct StreamView: NSViewRepresentable {
         view.endToEndMeter = endToEndMeter
         view.decodeMeter = decodeMeter
         view.displayMeter = displayMeter
+        view.onResizeTarget = onResizeTarget
+        view.onDecodedSize = onDecodedSize
         view.start(connection: connection, onFrame: onFrame, onSessionEnd: onSessionEnd)
         return view
     }
@@ -142,6 +150,8 @@ public struct StreamView: NSViewRepresentable {
         view.endToEndMeter = endToEndMeter
         view.decodeMeter = decodeMeter
         view.displayMeter = displayMeter
+        view.onResizeTarget = onResizeTarget
+        view.onDecodedSize = onDecodedSize
         // SwiftUI reuses the NSView across state changes — repoint the pump only when the
         // connection identity actually changed.
         if view.connection !== connection {
@@ -204,6 +214,13 @@ public final class StreamLayerView: NSView {
     /// view can't do that itself (the connection's owner disconnects).
     public var onDisconnectRequest: (() -> Void)?
 
+    /// Resize overlay signals (design/midstream-resolution-resize.md client UX): `onResizeTarget`
+    /// (main thread, via the follower) fires the instant the window starts steering toward a new
+    /// size; `onDecodedSize` (PUMP thread) fires when a new-mode IDR's dims land. The owner drives
+    /// the blur+spinner from these — set before `start()`.
+    public var onResizeTarget: ((UInt32, UInt32) -> Void)?
+    public var onDecodedSize: (@Sendable (Int, Int) -> Void)?
+
     /// Main-thread only. False = input capture disabled outright (UI layered over the
     /// stream); flipping to true auto-engages once.
     public var captureEnabled = true {
@@ -629,13 +646,16 @@ public final class StreamLayerView: NSView {
             displayMeter: displayMeter,
             makeDisplayLink: { displayLink(target: $0, selector: $1) },
             onFrame: onFrame,
-            onSessionEnd: onSessionEnd)
+            onSessionEnd: onSessionEnd,
+            onDecodedSize: onDecodedSize) // resize overlay END signal (new-mode IDR dims)
         // Match-window (C3): follow the window's pixel size when the setting is on. Latched at
         // session start (mirrors the other clients); the first real `layout()` feeds the initial
         // size, so the stream converges to the window even if the connect used the explicit mode.
-        matchFollower = MatchWindowFollower(
+        let follower = MatchWindowFollower(
             connection: connection,
             enabled: UserDefaults.standard.bool(forKey: DefaultsKey.matchWindow))
+        follower.onResizeTarget = onResizeTarget // resize overlay START signal (instant, on the follower)
+        matchFollower = follower
         layoutPresenter()
         requestAutoCapture() // entering a session is the deliberate "capture me" moment
     }