Fix Linux audio backend preference and worker footage render crash

- On Linux, automatically prefer PipeWire/JACK/PulseAudio over ALSA
  even when a saved ALSA device name exists in config.
- Restore Footage length after deserialization so worker snapshots
  have valid stream lengths and video playback can advance.
- Guard ResolveDecoderFromInput and ProcessAudioFootage against a
  null decoder cache to prevent worker crashes on direct Footage ->
  ViewerOutput connections.
- Keep Linux signal backtrace handler in the render worker.
- Add Oak project SVG logos.

app/render/renderprocessor.cpp

@@ -317,6 +317,12 @@ RenderProcessor::ResolveDecoderFromInput(const QString &decoder_id,
 		return nullptr;
 	}
 
+	if (!decoder_cache_) {
+		qWarning() << "Cannot resolve decoder for" << stream.filename()
+				   << "without a decoder cache";
+		return nullptr;
+	}
+
 	QMutexLocker locker(decoder_cache_->mutex());
 
 	DecoderPair decoder = decoder_cache_->value(stream);
@@ -599,6 +605,12 @@ void RenderProcessor::ProcessAudioFootage(SampleBuffer &destination,
 										  const FootageJob *stream,
 										  const TimeRange &input_time)
 {
+	// The worker process has no decoder cache and does not decode audio. Bail
+	// out gracefully rather than letting ResolveDecoderFromInput crash.
+	if (!decoder_cache_) {
+		return;
+	}
+
 	DecoderPtr decoder = ResolveDecoderFromInput(
 		stream->decoder(),
 		Decoder::CodecStream(stream->filename(),

app/render/worker/workermain.cpp

@@ -20,6 +20,7 @@
 
 #include <cstdio>
 #include <cstring>
+#include <csignal>
 #include <memory>
 #include <optional>
 
@@ -32,6 +33,11 @@
 #include <QOpenGLContext>
 #include <QSurfaceFormat>
 
+#ifdef Q_OS_LINUX
+#include <execinfo.h>
+#include <unistd.h>
+#endif
+
 #include "common/qtutils.h"
 #include "config/config.h"
 #include "core.h"
@@ -59,6 +65,18 @@ void HideWorkerDockIcon();
 namespace
 {
 
+#ifdef Q_OS_LINUX
+void PrintBacktrace(int sig)
+{
+	void *array[50];
+	size_t size = backtrace(array, 50);
+	fprintf(stderr, "worker: caught signal %d, backtrace:\n", sig);
+	backtrace_symbols_fd(array, size, STDERR_FILENO);
+	fflush(stderr);
+	_exit(128 + sig);
+}
+#endif
+
 constexpr int kProtocolVersion = 1;
 constexpr int kDefaultWidth = 1920;
 constexpr int kDefaultHeight = 1080;
@@ -606,6 +624,12 @@ int main(int argc, char *argv[])
 		}
 	}
 
+#ifdef Q_OS_LINUX
+	std::signal(SIGSEGV, PrintBacktrace);
+	std::signal(SIGABRT, PrintBacktrace);
+	std::signal(SIGFPE, PrintBacktrace);
+#endif
+
 	QFile in;
 	QFile out;
 	if (!in.open(stdin, QIODevice::ReadOnly | QIODevice::Unbuffered) ||