refactor(task,render): RenderTask family over a new oakrender ticket C ABI

- oakrender: new ticket family (render_frame/render_audio with finished
  callback, result frame/samples access, cancel/wait), project copier
  C API, cache get_invalidated_ranges, manager set_aggressive_gc
- oaknode: node_copy_inputs, set_value_hint_track, viewer params
  setters, video frame cache borrowed outlet, project copy_settings
- oakcodec: encoder desired pixel format, export format extension,
  encoding generate_matrix, custom range in encoding params POD
- oaktask: RenderTask orchestrates oakrender tickets (no Qt threads/
  watchers), PreCacheTask and ExportTask rewritten over the oaknode/
  oakrender/oakcodec C ABIs; frames cross from oakrender to oakcodec
  handles by pixel copy (different control blocks)
- the two-step texture/download render path collapses into single-step
  (tickets always yield frames); subtitle sidecar kept
- tests: 105 in build-oaktask (export/precache factory paths,
  construction, conform end-to-end); regressions all green

include/render/copier.h

@@ -0,0 +1,65 @@
+/***
+
+  Oak Video Editor - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  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/>.
+
+***/
+
+#ifndef OAK_EDITOR_RENDER_COPIER_H
+#define OAK_EDITOR_RENDER_COPIER_H
+
+#include "node/node.h"
+#include "node/project.h"
+#include "render/error.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Opaque handle to a project copier (olive::ProjectCopier):
+ *        deep-copies a project graph for background processing
+ *        (export/precache).
+ */
+typedef struct OakRenderProjectCopier OakRenderProjectCopier;
+
+/**
+ * @brief Create a copier. The copy is built by
+ *        oakrender_project_copier_set_project().
+ */
+OakRenderProjectCopier *oakrender_project_copier_create(void);
+
+/** @brief Free the copier AND its copied project. NULL-safe. */
+void oakrender_project_copier_free(OakRenderProjectCopier *copier);
+
+/** @brief (Re)build the copy from `project`. */
+int oakrender_project_copier_set_project(OakRenderProjectCopier *copier,
+										 OakNodeProject *project);
+
+/** @brief The copied counterpart of an original node (borrowed), NULL
+ *        when the node is not in the copied project. */
+OakNodeNode *oakrender_project_copier_get_copy(
+	OakRenderProjectCopier *copier, OakNodeNode *original);
+
+/** @brief The copied project (borrowed). */
+OakNodeProject *oakrender_project_copier_get_copied_project(
+	OakRenderProjectCopier *copier);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif //OAK_EDITOR_RENDER_COPIER_H