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.

ios/ReceiverTests/AvccConverterTests.swift

@@ -0,0 +1,27 @@
+import XCTest
+@testable import Receiver
+
+final class AvccConverterTests: XCTestCase {
+    func testNalUnits() {
+        let annexB: [UInt8] = [0, 0, 1, 0x41, 0x11, 0, 0, 1, 0x67, 0xAA]
+        XCTAssertEqual(AvccConverter.nalUnits(annexB), [[0x41, 0x11], [0x67, 0xAA]])
+    }
+
+    func testToAvcc() {
+        let annexB: [UInt8] = [0, 0, 1, 0x41, 0x11, 0, 0, 1, 0x67, 0xAA]
+        let avcc = AvccConverter.toAvcc(annexB)
+        XCTAssertEqual(avcc, [0, 0, 0, 2, 0x41, 0x11, 0, 0, 0, 2, 0x67, 0xAA])
+    }
+
+    func testFromAvccRoundtrip() {
+        let units: [[UInt8]] = [[0x41, 0x11], [0x67, 0xAA, 0xBB]]
+        let annexB = [0, 0, 1] + units[0] + [0, 0, 1] + units[1]
+        let avcc = AvccConverter.toAvcc(annexB)
+        XCTAssertEqual(AvccConverter.fromAvcc(avcc ?? []), units)
+    }
+
+    func testEmptyReturnsNil() {
+        XCTAssertNil(AvccConverter.toAvcc([UInt8]()))
+        XCTAssertNil(AvccConverter.toAvcc([0, 0, 1]))
+    }
+}