feat(audio): implement voice chat using Opus codec

Add voice chat support with Opus encoding/decoding, push-to-talk (V key), and new audio recording infrastructure.

cmake/modules/FindOpus.cmake

@@ -0,0 +1,25 @@
+include(FindPackageHandleStandardArgs)
+
+find_path(OPUS_INCLUDE_DIR
+    NAMES opus/opus.h opus.h
+)
+
+find_library(OPUS_LIBRARY
+    NAMES opus
+)
+
+find_package_handle_standard_args(
+    Opus
+    REQUIRED_VARS
+        OPUS_INCLUDE_DIR
+        OPUS_LIBRARY
+)
+
+if(Opus_FOUND)
+    add_library(Opus::Opus UNKNOWN IMPORTED)
+
+    set_target_properties(Opus::Opus PROPERTIES
+        IMPORTED_LOCATION "${OPUS_LIBRARY}"
+        INTERFACE_INCLUDE_DIRECTORIES "${OPUS_INCLUDE_DIR}"
+    )
+endif()