test: replace fake and duplicate tests with real assertions

Fake tests rewritten to assert real behavior:
- audio_smoke: conversion tests now actually Convert() samples and verify
  output; waveform length/summary assertions tightened to exact values
- plugin_format_conversion: RowBytes/U8ToU16/LoadImageFile now call real
  production code (VideoParams::GetBytesPerPixel, sws scaler, OIIO decode
  of tests/img.png with known pixel values)
- core_color: HSV round trip now verifies fromHsv(toHsv(c)) == c instead
  of comparing toHsv against its own accessors
- core_bezier/node_inputimmediate: expected values replaced with
  independently derived constants instead of re-running the code under test
- common_commandlineparser/common_debug/common_jobtime: capture
  stdout/stderr/qDebug and assert actual output content
- proxy_manager: ProxyFinished test now drives a real proxy job instead of
  emitting the signal itself; proxy_dialog/panel/proxy/preferences/timeruler
  tests assert real widget state
- viewer_smoke/preview_autocacher/render_misc: zero-assertion tests given
  observable-state assertions or removed where nothing is observable

Duplicates removed:
- plugin_smoke_test.cpp: 18 tests duplicated from plugin_paraminstance /
  plugin_support_* / plugin_renderer_readback (751 -> 180 lines)
- module_smoke HumanStrings tests covered precisely by ui_humanstrings_test
- render_misc duplicate kDefaultInterpolation constant check

Removed by policy (skip allowed, never disabled):
- all DISABLED_ prefixes: re-enabled as real offscreen tests or deleted
- ffmpeg_decoder_hw: hardcoded personal path replaced with
  OAK_TEST_HW_DECODE_FILE env var, GTEST_SKIP when unset

Also:
- config_test: restore Config defaults after run (cross-test pollution)
- render_worker_footage: drop /tmp debug-output scaffolding
- previewaudiodevice construction test asserts the real bugfix

tests/gtest/render_misc_test.cpp

@@ -466,9 +466,6 @@ TEST(TextureDummy, AccessorsAndNoOpIo)
 	EXPECT_FALSE(texture.IsJob());
 	EXPECT_EQ(texture.job(), nullptr);
 
-	EXPECT_EQ(int(olive::Texture::kDefaultInterpolation),
-			  int(olive::Texture::kMipmappedLinear));
-
 	char data[4] = {};
 	texture.Upload(data, 4);
 	texture.Download(data, 4);
@@ -683,14 +680,22 @@ TEST_F(RenderMiscAutoCacherTest,
 }
 
 // A conform-ready notification with no conform-blocked audio ranges must be a
-// harmless no-op.
+// harmless no-op: no cache jobs may be queued and no signals emitted.
 TEST_F(RenderMiscAutoCacherTest, ConformReadyWithoutPendingConformsIsNoOp)
 {
 	olive::PreviewAutoCacher cacher;
 	cacher.SetProject(project_.get());
 
+	QSignalSpy stop_spy(&cacher, &olive::PreviewAutoCacher::StopCacheProxyTasks);
+	QSignalSpy progress_spy(&cacher,
+							&olive::PreviewAutoCacher::SignalCacheProxyTaskProgress);
+
 	emit olive::ConformManager::instance()->ConformReady();
 
+	EXPECT_EQ(stop_spy.count(), 0);
+	EXPECT_EQ(progress_spy.count(), 0);
+	EXPECT_FALSE(cacher.IsRenderingCustomRange());
+
 	cacher.SetProject(nullptr);
 }
 
@@ -700,24 +705,34 @@ TEST_F(RenderMiscAutoCacherTest, CacheProxyTaskCancelledClearsPendingJobs)
 {
 	auto *viewer = new olive::ViewerOutput();
 	viewer->setParent(project_.get());
+	viewer->SetVideoParams(
+		olive::VideoParams(64, 64, olive::rational(1, 25),
+						   olive::PixelFormat::U8,
+						   olive::VideoParams::kRGBAChannelCount));
 
 	olive::PreviewAutoCacher cacher;
 
-	// No project is set, so the forced range sits in the pending queue.
+	// No project is set, so the forced range cannot be dispatched and sits in
+	// the pending queue
 	cacher.ForceCacheRange(
 		viewer, olive::TimeRange(olive::rational(0), olive::rational(1)));
+	EXPECT_TRUE(cacher.IsRenderingCustomRange());
 
 	EXPECT_TRUE(QMetaObject::invokeMethod(&cacher, "CacheProxyTaskCancelled",
 										  Qt::DirectConnection));
 
+	// With the pending jobs cleared, the custom range is no longer being
+	// rendered
+	EXPECT_FALSE(cacher.IsRenderingCustomRange());
+
 	cacher.SetProject(nullptr);
 }
 
 // With an unknown/dummy graphics backend the RenderManager never creates the
-// GPU-side objects. Those pointers must be null (previously they were left
-// uninitialized, so callers such as ViewerWidget dereferenced garbage and
-// crashed).
-TEST(RenderManagerDummyBackend, GpuMembersAreNullRatherThanUninitialized)
+// GPU-side objects. The auto-cacher pointer must be null (previously it was
+// left uninitialized, so callers such as ViewerWidget dereferenced garbage
+// and crashed).
+TEST(RenderManagerDummyBackend, GpuCacherMemberIsNullRatherThanUninitialized)
 {
 	const QVariant previous =
 		olive::Config::Current()[QStringLiteral("GraphicsBackend")];
@@ -726,6 +741,10 @@ TEST(RenderManagerDummyBackend, GpuMembersAreNullRatherThanUninitialized)
 
 	olive::RenderManager::CreateInstance();
 
+	EXPECT_EQ(olive::RenderManager::instance()->backend(),
+			  olive::RenderManager::kDummy);
+	EXPECT_EQ(olive::RenderManager::instance()->requested_backend(),
+			  olive::RenderManager::kDummy);
 	EXPECT_EQ(olive::RenderManager::instance()->GetCacher(), nullptr);
 
 	olive::RenderManager::DestroyInstance();