feat(clients): codec preference on Windows/Apple/Android clients (Phase 2b)

Rounds out codec negotiation across the last three clients — each advertises what it can decode,
builds its decoder from the resolved Welcome.codec, and exposes a "Video codec" preference picker.

**Windows** (Rust, mirrors Linux): `decodable_codecs()` + `ffmpeg_codec_id()`; the D3D11VA and
software FFmpeg decoders (and the mid-session D3D11VA→software demotion) open the negotiated codec
instead of hardcoding HEVC; settings gain a `codec` field + reactor ComboBox; `--codec` CLI flag.

**Apple** (Swift/C-ABI): AnnexB is now codec-aware — a `VideoCodec` enum drives H.264 vs HEVC NAL
parsing / parameter-set extraction (`CMVideoFormatDescriptionCreateFromH264ParameterSets` for H.264,
no VPS) and AVCC repacking; `PunktfunkConnection` advertises H264|HEVC via `punktfunk_connect_ex7`,
reads `resolvedCodec` (`punktfunk_connection_codec`), and threads `videoCodec` into the stage-1/2
pipelines + `VideoDecoder`; SettingsView "Video codec" Picker (auto/HEVC/H.264). AV1 is left out
(hosts don't emit it on the native path, and it's not an AnnexB codec). Test call sites updated.

**Android** (Kotlin + Rust JNI): the JNI `nativeConnect` gains `preferredCodec`; the native decode
loop picks the AMediaCodec MIME (`video/hevc`|`video/avc`) from `connector.codec` and advertises
H264|HEVC; Settings `codec` field + Compose dropdown.

Core/host/probe/Linux clippy + tests green (unchanged from 2a). Windows/Apple/Android compile on
their platform CI (this Linux box can't build them — Windows toolchain / Xcode / the Android NDK's
opus-cmake toolchain). All follow the Linux client's validated pattern.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/ContentView.swift

@@ -28,10 +28,20 @@ struct ContentView: View {
     @AppStorage(DefaultsKey.gamepadType) private var gamepadType = 0
     @AppStorage(DefaultsKey.bitrateKbps) private var bitrateKbps = 0
     @AppStorage(DefaultsKey.audioChannels) private var audioChannels = 2
+    @AppStorage(DefaultsKey.codec) private var codec = "auto"
     @AppStorage(DefaultsKey.hdrEnabled) private var hdrEnabled = true
     @AppStorage(DefaultsKey.fullscreenWhileStreaming) private var fullscreenWhileStreaming = true
     @AppStorage(DefaultsKey.hudEnabled) private var hudEnabled = true
     @AppStorage(DefaultsKey.hudPlacement) private var hudPlacement = HUDPlacement.topTrailing.rawValue
+    /// The `codec` setting as a `PUNKTFUNK_CODEC_*` soft-preference byte (`0` = auto).
+    private var preferredCodecByte: UInt8 {
+        switch codec {
+        case "h264": return PunktfunkConnection.codecH264
+        case "hevc": return PunktfunkConnection.codecHEVC
+        case "av1": return PunktfunkConnection.codecAV1
+        default: return 0
+        }
+    }
     @State private var showAddHost = false
     @State private var pairingTarget: StoredHost?
     /// A fresh `pair=required`/unknown host the user tapped: drives the choice between no-PIN
@@ -378,6 +388,7 @@ struct ContentView: View {
             bitrateKbps: UInt32(clamping: bitrateKbps),
             audioChannels: UInt8(clamping: audioChannels),
             hdrEnabled: hdrEnabled,
+            preferredCodec: preferredCodecByte,
             launchID: launchID,
             allowTofu: allowTofu,
             requestAccess: requestAccess)
@@ -521,6 +532,7 @@ struct ContentView: View {
             bitrateKbps: bitrate,
             audioChannels: UInt8(clamping: audioChannels),
             hdrEnabled: hdrEnabled,
+            preferredCodec: preferredCodecByte,
             autoTrust: true)
     }
 }