build: split the engine into liboakengine.so; worker drops the UI entirely

Physical split: app/{audio,cli,codec,common,config,node,pluginSupport,
render,task,timeline,undo,tool,shaders} plus coreengine, version and
ui/icons+colorcoding move to a new top-level engine/ tree, built as
liboakengine.so (shared). The render backends (oakgl/oakvulkan) move
with it and link the engine library instead of embedding a static
render-core subset (libolive-rendercore is gone).

- oak-render-worker now links liboakengine instead of the whole
  libolive-editor object set: 336MB -> 2.9MB, no Qt Widgets UI
- the editor links liboakengine for the engine and keeps only UI
  objects in libolive-editor
- install/packaging: GNUInstallDirs libdir on Linux, bundle copy on
  macOS, oakengine.dll staged for NSIS, AppImage validation entry
- fix backend lookup for the new layout: DynamicRenderer searched
  ../app but backends now live in engine/; a stale pre-split liboakgl
  in the build tree got dlopened instead, re-initialized and later
  destroyed the interposed engine statics (full-suite segfault at
  DialogSequenceParameterTab, found via gdb watchpoint)

engine/codec/exportcodec.cpp

@@ -0,0 +1,139 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2022 Olive Team
+  Modifications Copyright (C) 2025 mikesolar
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#include "exportcodec.h"
+
+extern "C" {
+}
+
+namespace olive
+{
+
+QString ExportCodec::get_codec_name(ExportCodec::Codec c)
+{
+	switch (c) {
+	case k_codec_d_nx_hd:
+		return tr("DNxHD");
+	case k_codec_h264:
+		return tr("H.264");
+	case k_codec_h264rgb:
+		return tr("H.264 RGB");
+	case k_codec_h265:
+		return tr("H.265");
+	case k_codec_open_exr:
+		return tr("OpenEXR");
+	case k_codec_png:
+		return tr("PNG");
+	case k_codec_pro_res:
+		return tr("ProRes");
+	case k_codec_cineform:
+		return tr("Cineform");
+	case k_codec_tiff:
+		return tr("TIFF");
+	case k_codec_m_p2:
+		return tr("MP2");
+	case k_codec_m_p3:
+		return tr("MP3");
+	case k_codec_aac:
+		return tr("AAC");
+	case k_codec_pcm:
+		return tr("PCM (Uncompressed)");
+	case k_codec_flac:
+		return tr("FLAC");
+	case k_codec_opus:
+		return tr("Opus");
+	case k_codec_vorbis:
+		return tr("Vorbis");
+	case k_codec_v_p9:
+		return tr("VP9");
+	case k_codec_a_v1:
+		return tr("AV1");
+	case k_codec_srt:
+		return tr("SubRip SRT");
+	case k_codec_count:
+		break;
+	}
+
+	return tr("Unknown");
+}
+
+bool ExportCodec::is_codec_a_still_image(ExportCodec::Codec c)
+{
+	switch (c) {
+	case k_codec_d_nx_hd:
+	case k_codec_h264:
+	case k_codec_h264rgb:
+	case k_codec_h265:
+	case k_codec_pro_res:
+	case k_codec_cineform:
+	case k_codec_m_p2:
+	case k_codec_m_p3:
+	case k_codec_aac:
+	case k_codec_pcm:
+	case k_codec_vorbis:
+	case k_codec_opus:
+	case k_codec_flac:
+	case k_codec_v_p9:
+	case k_codec_a_v1:
+	case k_codec_srt:
+		return false;
+	case k_codec_open_exr:
+	case k_codec_png:
+	case k_codec_tiff:
+		return true;
+	case k_codec_count:
+		break;
+	}
+
+	return false;
+}
+
+bool ExportCodec::is_codec_lossless(Codec c)
+{
+	switch (c) {
+	case k_codec_pcm:
+	case k_codec_flac:
+		return true;
+	case k_codec_d_nx_hd:
+	case k_codec_h264:
+	case k_codec_h264rgb:
+	case k_codec_h265:
+	case k_codec_pro_res:
+	case k_codec_cineform:
+	case k_codec_m_p2:
+	case k_codec_m_p3:
+	case k_codec_aac:
+	case k_codec_vorbis:
+	case k_codec_opus:
+	case k_codec_v_p9:
+	case k_codec_a_v1:
+	case k_codec_srt:
+	case k_codec_open_exr:
+	case k_codec_png:
+	case k_codec_tiff:
+	case k_codec_count:
+		break;
+	}
+
+	return false;
+}
+
+}