[AudioIn] Answer sceAudioInGetSilentState without an input backend

No AudioIn port can be opened until an input backend exists, so the export
returns an AudioIn error code (0x80260101) instead of being an unresolved
import.

src/SharpEmu.Libs/Audio/AudioInExports.cs

@@ -0,0 +1,18 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.HLE;
+
+namespace SharpEmu.Libs.Audio;
+
+public static class AudioInExports
+{
+    [SysAbiExport(
+        Nid = "BohEAQ7DlUE",
+        ExportName = "sceAudioInGetSilentState",
+        Target = Generation.Gen4 | Generation.Gen5,
+        LibraryName = "libSceAudioIn")]
+    public static int GetSilentState(CpuContext ctx) =>
+        // No AudioIn ports can be opened until an input backend is implemented.
+        ctx.SetReturn(unchecked((int)0x80260101));
+}