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/proxy_dialog_test.cpp

@@ -1,5 +1,9 @@
 #include <gtest/gtest.h>
 
+#include <QCheckBox>
+#include <QPushButton>
+#include <QTreeWidget>
+
 #include "config/config.h"
 #include "dialog/proxy/proxydialog.h"
 #include "node/project/footage/footage.h"
@@ -35,11 +39,45 @@ TEST(ProxyDialog, ConstructsInGlobalModeWithNullParent)
 
 TEST(ProxyDialog, ConstructsWithFootageList)
 {
-	olive::Footage footage;
+	olive::Footage footage(QStringLiteral("/tmp/oak-proxy-test.mov"));
 	const QVector<olive::Footage *> items = { &footage };
 
 	olive::ProxyDialog dialog(nullptr, items);
-	SUCCEED();
+	EXPECT_EQ(dialog.windowTitle(), QStringLiteral("Proxy Settings"));
+
+	// Global mode has no footage tree at all
+	olive::ProxyDialog global_dialog(nullptr);
+	EXPECT_EQ(global_dialog.findChild<QTreeWidget *>(), nullptr);
+
+	// Footage mode shows one tree row per item with its proxy state
+	auto *tree = dialog.findChild<QTreeWidget *>();
+	ASSERT_NE(tree, nullptr);
+	ASSERT_EQ(tree->topLevelItemCount(), 1);
+	EXPECT_EQ(tree->topLevelItem(0)->text(0),
+			  QStringLiteral("/tmp/oak-proxy-test.mov"));
+	EXPECT_EQ(tree->topLevelItem(0)->text(1), QStringLiteral("missing"));
+
+	// Fresh footage has no custom params, so the custom settings checkbox
+	// starts unchecked
+	QCheckBox *custom_checkbox = nullptr;
+	foreach (QCheckBox *box, dialog.findChildren<QCheckBox *>()) {
+		if (box->text() ==
+			QStringLiteral("Use custom settings for selected footage")) {
+			custom_checkbox = box;
+			break;
+		}
+	}
+	ASSERT_NE(custom_checkbox, nullptr);
+	EXPECT_FALSE(custom_checkbox->isChecked());
+
+	// Footage mode adds generate/delete actions next to Close
+	QStringList button_texts;
+	foreach (QPushButton *b, dialog.findChildren<QPushButton *>()) {
+		button_texts << b->text();
+	}
+	EXPECT_TRUE(button_texts.contains(QStringLiteral("Generate Proxies")));
+	EXPECT_TRUE(button_texts.contains(QStringLiteral("Delete Proxies")));
+	EXPECT_TRUE(button_texts.contains(QStringLiteral("Close")));
 }
 
 TEST(ProxyDialog, AcceptSavesGlobalSettingsToConfig)