feat(resize/apple): Match-window mid-stream resize trigger + settings (C3)

design/midstream-resolution-resize.md Phase 2, Apple client. The stream mode
follows the session window/scene: a windowed macOS window resize or an iPad
Stage Manager / Split View scene change renegotiates the host's virtual
display + encoder via the existing PunktfunkConnection.requestMode, so a
windowed session streams native-resolution pixels instead of scaling.
Decode/present need nothing — VideoToolbox recreates its session on the
keyframe-derived format-description change (§1 table).

- MatchWindowFollower (new): the shared D2 trigger discipline — physical
  pixels even-floored + clamped ≥320×200, debounce to resize-end, ≥1 s
  between requests, skip a size equal to the live mode, request each distinct
  size at most once (stops re-asking a rejected size / looping on a host
  rollback). Pure normalize/request core is unit-tested (MatchWindowTests).
- macOS StreamLayerView: fed from layoutPresenter() (bounds → convertToBacking),
  guarded to once-in-a-window.
- iOS StreamViewController: fed from viewDidLayoutSubviews (bounds × render
  scale); iOS-only (iPhone fullscreen no-ops, tvOS uses AVDisplayManager).
- Settings: "Match window" toggle in the Stream mode section (iOS + macOS),
  DefaultsKey.matchWindow, read per session by the follower.

Verified on a Linux Swift 6.1.2 toolchain (the app target needs AppKit/UIKit,
unavailable here): the real MatchWindowFollower.swift type-checks in Swift 5
mode against a connection stub, and the pure discipline + the follower's
decision path pass a standalone harness (drag-settle + grow → exactly two
switches, refresh preserved, no re-request loop). A full build + on-device run
(macOS window, iPad Stage Manager) remains for a Mac.

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

clients/apple/Tests/PunktfunkKitTests/MatchWindowTests.swift

@@ -0,0 +1,43 @@
+// The Match-window trigger discipline (design/midstream-resolution-resize.md D2), as pure
+// functions — the same rules the session binary's `resize_decision` unit-tests: physical pixels
+// even-floored and clamped ≥ 320×200, skip a size equal to the live mode, and request each
+// distinct size at most once (so a rejected size / a host rollback can't loop).
+
+import XCTest
+
+@testable import PunktfunkKit
+
+final class MatchWindowTests: XCTestCase {
+    func testNormalizeEvenFloorsAndClamps() {
+        // Odd pixels floor to even (the host rejects odd dimensions).
+        let a = MatchWindow.normalize(widthPx: 1001, heightPx: 601)
+        XCTAssertEqual(a.width, 1000)
+        XCTAssertEqual(a.height, 600)
+        // Already-even sizes pass through.
+        let b = MatchWindow.normalize(widthPx: 2560, heightPx: 1440)
+        XCTAssertEqual(b.width, 2560)
+        XCTAssertEqual(b.height, 1440)
+        // Tiny / zero clamp to the host floor.
+        let c = MatchWindow.normalize(widthPx: 100, heightPx: 80)
+        XCTAssertEqual(c.width, 320)
+        XCTAssertEqual(c.height, 200)
+        let z = MatchWindow.normalize(widthPx: 0, heightPx: -4)
+        XCTAssertEqual(z.width, 320)
+        XCTAssertEqual(z.height, 200)
+    }
+
+    func testRequestSkipsEqualAndAlreadyRequested() {
+        // A new size (different from the live mode, not yet requested) → request it.
+        let r = MatchWindow.request(
+            target: (1000, 600), current: (1280, 720), lastRequested: (800, 500))
+        XCTAssertEqual(r?.width, 1000)
+        XCTAssertEqual(r?.height, 600)
+        // Equal to the live mode → nothing to do.
+        XCTAssertNil(MatchWindow.request(
+            target: (1280, 720), current: (1280, 720), lastRequested: nil))
+        // Already requested once → don't re-ask (covers a rejected size AND a host rollback:
+        // accepted → rebuild failed → corrective ack restored the old mode must not loop).
+        XCTAssertNil(MatchWindow.request(
+            target: (1000, 600), current: (1280, 720), lastRequested: (1000, 600)))
+    }
+}