feat(codec): make client codec selection real — GPU-aware native advertisement

The clients' codec pickers sent a preference the host threw away:
host_wire_caps() hardcoded HEVC for every GPU backend, so the native
path never emitted H.264/AV1 regardless of what the user chose.

Host: advertise what the backend actually encodes, mirroring the
GameStream serverinfo logic — software openh264 emits H.264; probed
backends (Linux VAAPI, Windows AMF/QSV) advertise their per-GPU
CodecSupport via the new wire_mask(); NVENC keeps the
Moonlight-validated H.264|HEVC|AV1 static superset; an empty probe
falls back to the superset so auto clients still resolve HEVC. Gate
10-bit to HEVC (like the 4:4:4 gate) now that a client can steer the
codec — Main10 is the only 10-bit encode path. Fix the web-console
stats label hardcoded to "hevc" (new Codec::label(), shared with the
GameStream register_session mapping).

Android: replace the hardcoded H264|HEVC Hello advertisement with a
videoCodecs param fed by VideoDecoders.decodableCodecBits() (AV1 bit
only when a real hardware video/av01 decoder exists — the decode loop
was already mime-driven); offer AV1 in the codec picker on capable
devices.

Decky: add the missing "Video codec" dropdown (auto/hevc/h264/av1) to
the plugin settings, round-tripping the same codec key the flatpak
client reads.

Apple: unchanged by design (AnnexB.swift is NAL-only, AV1 is never
advertised); refresh the stale "hosts don't emit AV1 on the native
path yet" comments here and host-side.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/android/app/src/main/kotlin/io/unom/punktfunk/HostConnect.kt

@@ -3,6 +3,7 @@ package io.unom.punktfunk
 import android.content.Context
 import io.unom.punktfunk.kit.Gamepad
 import io.unom.punktfunk.kit.NativeBridge
+import io.unom.punktfunk.kit.VideoDecoders
 import io.unom.punktfunk.kit.security.ClientIdentity
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
@@ -41,7 +42,10 @@ suspend fun connectToHost(
             host, port, w, h, hz,
             identity.certPem, identity.privateKeyPem, pinHex,
             settings.bitrateKbps, settings.compositor, gamepadPref,
-            hdrEnabled, settings.audioChannels, settings.preferredCodec(), timeoutMs,
+            hdrEnabled, settings.audioChannels,
+            // What this device can decode (H.264|HEVC always, AV1 when a real decoder exists) +
+            // the user's soft codec preference — the host resolves the emitted codec from both.
+            VideoDecoders.decodableCodecBits(), settings.preferredCodec(), timeoutMs,
             launch,
         )
     }

clients/android/app/src/main/kotlin/io/unom/punktfunk/Settings.kt

@@ -26,8 +26,9 @@ data class Settings(
     /** Requested audio channel count: 2 (stereo), 6 (5.1) or 8 (7.1). The host clamps to what it
      * can capture; the resolved count drives the decoder + AAudio layout. */
     val audioChannels: Int = 2,
-    /** Preferred video codec: `"auto"` (host decides), `"hevc"`, or `"h264"`. A soft preference — the
-     * host emits it when it can, else falls back. AMediaCodec decodes whichever the host resolves. */
+    /** Preferred video codec: `"auto"` (host decides), `"hevc"`, `"h264"`, or `"av1"`. A soft
+     * preference — the host emits it when it can, else falls back. AMediaCodec decodes whichever
+     * the host resolves (AV1 is only advertised/offered when the device has a real AV1 decoder). */
     val codec: String = "auto",
     val micEnabled: Boolean = false,
     /**
@@ -271,14 +272,17 @@ val AUDIO_CHANNEL_OPTIONS = listOf(
     8 to "7.1 Surround",
 )
 
-/** (stored value, label) for the preferred video codec. `"auto"` = host decides. */
+/** (stored value, label) for the preferred video codec. `"auto"` = host decides. The `"av1"` row
+ * only makes sense on a device with a real AV1 decoder — SettingsScreen filters it out otherwise. */
 val CODEC_OPTIONS = listOf(
     "auto" to "Automatic",
     "hevc" to "HEVC (H.265)",
     "h264" to "H.264 (AVC)",
+    "av1" to "AV1",
 )
 
-/** The [Settings.codec] string as a `quic::CODEC_*` preference byte (`0` = auto). H264=1, HEVC=2. */
+/** The [Settings.codec] string as a `quic::CODEC_*` preference byte (`0` = auto). H264=1, HEVC=2,
+ * AV1=4. */
 fun Settings.preferredCodec(): Int = when (codec) {
     "h264" -> 1
     "hevc" -> 2

clients/android/app/src/main/kotlin/io/unom/punktfunk/SettingsScreen.kt

@@ -65,6 +65,7 @@ import androidx.compose.ui.graphics.vector.ImageVector
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.dp
 import androidx.core.content.ContextCompat
+import io.unom.punktfunk.kit.VideoDecoders
 
 /**
  * Stream settings, organised as an iOS-Settings / Android-system-settings style list of category
@@ -300,7 +301,12 @@ private fun DisplaySettings(s: Settings, update: (Settings) -> Unit, context: an
             update(s.copy(bitrateKbps = kbps))
         }
 
-        SettingDropdown(label = "Video codec", options = CODEC_OPTIONS, selected = s.codec) { c ->
+        // AV1 is only offered when the device has a real AV1 decoder (it's never advertised to the
+        // host otherwise, so preferring it would be a dead setting). A stored "av1" from a capable
+        // device stays visible so the selection is always representable.
+        val av1Capable = remember { VideoDecoders.pickDecoder("video/av01") != null }
+        val codecOptions = CODEC_OPTIONS.filter { (v, _) -> v != "av1" || av1Capable || s.codec == "av1" }
+        SettingDropdown(label = "Video codec", options = codecOptions, selected = s.codec) { c ->
             update(s.copy(codec = c))
         }