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/timeline_waveform_sync_test.cpp

@@ -78,21 +78,21 @@ TEST(TimelineWaveformSync, ExtractEnvelopeUsesOnlyValidatedRanges)
 	// 3 seconds at 20 windows per second == 60 windows.
 	EXPECT_EQ(envelope.size(), 60);
 
-	// Window before the validated region should be silent.
-	EXPECT_DOUBLE_EQ(envelope.at(0), 0.0);
-
-	// Windows inside the validated region should have a non-zero peak.
-	bool found_nonzero = false;
-	for (int i = 20; i < 40; ++i) {
-		if (envelope.at(i) > 0.0) {
-			found_nonzero = true;
-			break;
-		}
+	// Windows before the validated region are silent placeholders
+	for (int i = 0; i < 20; ++i) {
+		EXPECT_DOUBLE_EQ(envelope.at(i), 0.0);
 	}
-	EXPECT_TRUE(found_nonzero);
 
-	// Window after the validated region should also be silent.
-	EXPECT_DOUBLE_EQ(envelope.at(59), 0.0);
+	// The validated second was filled with a constant 1.0 signal, so every
+	// window inside it must peak at exactly 1.0
+	for (int i = 20; i < 40; ++i) {
+		EXPECT_DOUBLE_EQ(envelope.at(i), 1.0);
+	}
+
+	// Windows after the validated region are silent placeholders too
+	for (int i = 40; i < 60; ++i) {
+		EXPECT_DOUBLE_EQ(envelope.at(i), 0.0);
+	}
 }
 
 TEST(TimelineWaveformSync, ExtractEnvelopeReportsValidityMask)