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.

.gitignore

@@ -19,6 +19,11 @@ compile_commands.json
 # Smoke test output
 *.h264
 
+# iOS (generated by bootstrap.sh / XcodeGen; project.yml is the source of truth)
+ios/Receiver.xcodeproj/
+ios/tools/
+ios/Receiver/Info.plist
+
 # IDE
 .vscode/
 .idea/