feat(ios): native receiver app (Swift, min iOS 17)

A native iOS receiver so an iPhone can act as the second receiver, speaking the existing signaling + RTP protocol (no C++ changes) and mirroring the Android receiver (Phase 8) source-to-source.

- RTP core (header/packet, jitter buffer, H.264 depacketizer) ported from the Android receiver
- BSD-socket signaling server (dual-stack, most-recent-peer, never-throwing sends) + NSBonjourServices
- VideoToolbox H.264 decode (in-band SPS/PPS, real-time, rebuilds on size change) -> AVSampleBufferDisplayLayer
- PLI keyframe recovery (500 ms) + pendingOffer for late surface attach
- XcodeGen project + bootstrap.sh; XCTest port of the Android suite + new coverage
- .gitignore for generated artifacts; CHANGELOG; PHASES + MEMORY updated

Status: authored; on-device validation pending a Mac + Xcode 26 + iPhone 16.

docs/PHASES.md

@@ -132,6 +132,33 @@ existing signaling + RTP protocol; no C++ changes.
 `--send --target window --peer <phone>:5005` rendered fullscreen on the
 phone (and HDMI via DP-alt-mode) with loss recovery.
 
+## Phase 9 — iOS Receiver App
+
+**Goal**: a native iOS receiver app (Swift) so an iPhone can act as the second
+receiver. The app speaks the existing signaling + RTP protocol; no C++ changes.
+Mirrors the Android receiver (Phase 8) source-to-source.
+
+- [x] 9.1 Xcode project scaffolding (`ios/`, XcodeGen spec + bootstrap script;
+      Info.plist with local-network + Bonjour privacy keys)
+- [x] 9.2 Swift protocol core + XCTest (rtp header/packet, jitter, depacketizer
+      ported source-to-source; added signaling JSON, line framing, AVCC, NAL
+      extraction tests — the Android side had no signaling tests)
+- [x] 9.3 Signaling server (BSD sockets, dual-stack, most-recent-peer, never
+      throws) + `NSBonjourServices` advertisement
+- [x] 9.4 Media path: UDP (poll-based) → jitter → depacketize → VideoToolbox
+      (in-band SPS/PPS, real-time decode) → AVSampleBufferDisplayLayer
+      (letterbox) + PLI on damage + pendingOffer for late surface attach
+- [ ] 9.5 On-device validation (needs a Mac + Xcode 26 + iPhone 16): unit tests
+      green on the simulator; `--discover` lists the phone; `--send --peer
+      <ip>:5005` streams letterboxed; PLI recovery on Wi-Fi loss
+- [ ] 9.6 Docs: iOS RUNBOOK quirks, README receiver section, PHASES + MEMORY
+
+**Validation**: `ios/bootstrap.sh test` (simulator) green; live session
+`--send --peer <iphone>:5005` renders fullscreen letterboxed on the iPhone with
+loss recovery. Note: this box is Linux — no Xcode/iOS SDK — so 9.2–9.4 are
+authored but only 9.5 can validate the VideoToolbox + local-network paths.
+
 ## Current phase
 
-Phase 8 — Android Receiver App (complete).
+Phase 9 — iOS Receiver App (implementation authored; on-device validation
+pending a Mac + Xcode 26 + iPhone 16).