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/task_cache_test.cpp

@@ -154,6 +154,25 @@ protected:
 	std::unique_ptr<olive::Project> project_;
 };
 
+namespace
+{
+
+// Exposes RenderTask's protected accessors so the test can inspect the
+// private viewer the task builds.
+class InspectablePreCacheTask : public olive::PreCacheTask {
+public:
+	InspectablePreCacheTask(olive::Footage *footage, int index,
+							olive::Sequence *sequence)
+		: PreCacheTask(footage, index, sequence)
+	{
+	}
+
+	using olive::RenderTask::video_params;
+	using olive::RenderTask::viewer;
+};
+
+} // namespace
+
 TEST_F(TaskPreCacheTest, ConstructorCopiesFootageIntoPrivateProject)
 {
 	const QString path = QDir(QStringLiteral(OAK_TEST_SOURCE_DIR))
@@ -171,8 +190,27 @@ TEST_F(TaskPreCacheTest, ConstructorCopiesFootageIntoPrivateProject)
 	// Construction copies the footage into a private project and wires it to a
 	// private viewer; it must not touch the render pipeline. Run() itself is
 	// not exercised here since it requires live render workers.
-	olive::PreCacheTask task(footage, 0, sequence);
+	InspectablePreCacheTask task(footage, 0, sequence);
 
 	EXPECT_TRUE(task.GetTitle().contains(path));
 	EXPECT_TRUE(task.GetTitle().contains(QStringLiteral(":0")));
+
+	// The private viewer must mirror the sequence's parameters
+	olive::ViewerOutput *viewer = task.viewer();
+	ASSERT_NE(viewer, nullptr);
+	EXPECT_EQ(task.video_params(), sequence->GetVideoParams());
+	EXPECT_EQ(viewer->GetVideoParams(), sequence->GetVideoParams());
+
+	// The viewer's texture input must be fed by a private copy of the footage:
+	// same file, different node, living in the task's private project rather
+	// than the caller's
+	olive::Node *connected = viewer->GetConnectedTextureOutput();
+	ASSERT_NE(connected, nullptr);
+	EXPECT_NE(connected, footage);
+
+	auto *copied_footage = dynamic_cast<olive::Footage *>(connected);
+	ASSERT_NE(copied_footage, nullptr);
+	EXPECT_EQ(copied_footage->filename(), footage->filename());
+	EXPECT_NE(copied_footage->project(), project_.get());
+	EXPECT_EQ(copied_footage->project(), viewer->project());
 }