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/Tests/PunktfunkKitTests/RemoteFirstLightTests.swift

@@ -138,7 +138,7 @@ final class RemoteFirstLightTests: XCTestCase {
             if firstPtsNs == 0 { firstPtsNs = au.ptsNs }
             lastPtsNs = au.ptsNs
 
-            if let f = AnnexB.formatDescription(fromIDR: au.data) {
+            if let f = AnnexB.formatDescription(fromIDR: au.data, codec: .hevc) {
                 format = f
                 if decoder == nil {
                     let dims = CMVideoFormatDescriptionGetDimensions(f)
@@ -155,7 +155,7 @@ final class RemoteFirstLightTests: XCTestCase {
                 }
             }
             guard let f = format, let dec = decoder,
-                  let sample = AnnexB.sampleBuffer(au: au, format: f)
+                  let sample = AnnexB.sampleBuffer(au: au, format: f, codec: .hevc)
             else { continue }
 
             var gotPixels = false