app: route all FFmpeg access through the ffmpeg_bridge C API

Replace every direct FFmpeg call in the editor and the render worker
with the pure C ffmpeg_bridge API, wrapped in thin C++ adapters that
preserve the original interfaces:

- avframeptr.h: olive::AVFrame adapter around FBFrame handles
- ffmpegutils: format conversion helpers on FB_* constants; the int
  overload is renamed GetCompatibleBridgePixelFormat to avoid a silent
  overload-resolution trap with the PixelFormat enum
- ffmpegdecoder/ffmpegencoder: rewritten as handle-based adapters over
  FBDecoder/FBProbe/FBEncoder/FBScaler/FBResampler
- audioprocessor: FBAudioGraph push/pull adapter
- pluginrenderer/OliveClip: sws/pixdesc usage converted to FBScaler and
  fb_pix_fmt_* queries
- AudioParams/channel layouts are plain uint64_t masks everywhere

Build integration: the root project no longer links FFMPEG directly;
only ffmpeg_bridge does. Binaries resolve the bridge library at runtime
via @loader_path inside the macOS app bundle (copied there post-build)
and via $ORIGIN/../ffmpeg_bridge/bin on Linux; on Windows the DLL is
installed next to the executables, so packages on all three platforms
ship the bridge library.

ffmpeg_bridge gains the extra API the adapters need:
fb_frame_make_writable, fb_decoder_get_format_duration,
fb_resampler_convert_frame, FB_PIX_FMT_YUV440P, SRT validation in
fb_probe_read_subtitle_stream, packed/planar fixes in
fb_encoder_write_audio, and a component-size fix in
fb_pix_fmt_component_size.

app/audio/audioprocessor.h

@@ -26,9 +26,7 @@
 #include <olive/core/core.h>
 #include <QByteArray>
 
-extern "C" {
-#include <libavfilter/avfilter.h>
-}
+#include <ffmpeg_bridge/ffmpeg_bridge.h>
 
 #include "common/define.h"
 
@@ -52,7 +50,7 @@ public:
 
 	bool IsOpen() const
 	{
-		return filter_graph_;
+		return graph_;
 	}
 
 	using Buffer = QVector<QByteArray>;
@@ -70,25 +68,13 @@ public:
 	}
 
 private:
-	static AVFilterContext *CreateTempoFilter(AVFilterGraph *graph,
-											  AVFilterContext *link,
-											  const double &tempo);
-
-	AVFilterGraph *filter_graph_;
-
-	AVFilterContext *buffersrc_ctx_;
-
-	AVFilterContext *buffersink_ctx_;
+	FBAudioGraph *graph_;
 
 	AudioParams from_;
-	AVSampleFormat from_fmt_;
 
 	AudioParams to_;
-	AVSampleFormat to_fmt_;
 
-	AVFrame *in_frame_;
-
-	AVFrame *out_frame_;
+	FBFrame *out_frame_;
 };
 
 }