refactor(timeline): de-Qt oaktimeline and wrap it in a pure C ABI

- de-Qt all 11 sources: markers/workarea lose QObject/signals (list
  re-sort via direct resort() call, drawing moves to the app layer),
  explicit unique_ptr ownership for marker lists and viewer's
  workarea/markers
- timeline undo command families (split/pointer/ripple/general/track)
  now hold oaknode C handles and do all graph work through the oaknode
  C ABI (no adapter layer); gaps are attached to the project graph
  before insertion, orphan handles tracked and freed
- fix the de-Qt severed Block->Track length-changed chain with a
  direct block_length_changed() call (positions were stale after
  split/trim)
- expand oaknode C API by ~20 functions needed by timeline
  (copy_in_graph, block kind/casts, connect_element, input arrays,
  tracklist family, marker/workarea borrowed outlets)
- pure C ABI in include/timeline (marker/workarea/edit, command
  factories returning OakUndoCommand), oakcommon XML get_native
  accessors
- oaknode<->oaktimeline resolve each other at runtime; standalone
  drivers link both into test binaries
- tests: oaktimeline 117, regressions oakcommon 193 / oaknode 96 /
  oakrender 42 / oakcodec 18 / oakaudio 36 all green

include/timeline/workarea.h

@@ -0,0 +1,92 @@
+/***
+
+  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_TIMELINE_WORKAREA_H
+#define OAK_EDITOR_TIMELINE_WORKAREA_H
+
+#include "common/xmlutils.h"
+#include "node/node.h"
+#include "timeline/error.h"
+#include "undo/undocommand.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Borrowed handle to a timeline work area
+ * (olive::TimelineWorkArea), owned by a viewer node.
+ */
+typedef struct OakTimelineWorkArea OakTimelineWorkArea;
+
+/**
+ * @brief Borrowed work area of a viewer node (sequence). NULL for NULL
+ * or when the node is not a viewer.
+ */
+OakTimelineWorkArea *oaktimeline_workarea_of(OakNodeNode *owner);
+
+/**
+ * @brief Read the work area state. Out params may individually be NULL.
+ */
+int oaktimeline_workarea_get(const OakTimelineWorkArea *w, int *in_num,
+							 int *in_den, int *out_num, int *out_den,
+							 int *enabled);
+
+/**
+ * @brief Set the range directly (live).
+ */
+int oaktimeline_workarea_set_range(OakTimelineWorkArea *w, int in_num,
+								   int in_den, int out_num, int out_den);
+
+/**
+ * @brief Create a set-range command (olive::WorkareaSetRangeCommand).
+ * The old range must be supplied by the caller (facade knows what it
+ * changed from). Owned; free with oakundo_command_free().
+ */
+OakUndoCommand *oaktimeline_workarea_set_range_command(
+	OakTimelineWorkArea *w, int in_num, int in_den, int out_num,
+	int out_den, int old_in_num, int old_in_den, int old_out_num,
+	int old_out_den);
+
+/**
+ * @brief Create a set-enabled command (olive::WorkareaSetEnabledCommand).
+ */
+OakUndoCommand *oaktimeline_workarea_set_enabled_command(
+	OakTimelineWorkArea *w, int enabled);
+
+/**
+ * @brief The reset sentinel range (TimelineWorkArea::k_reset_in/out).
+ */
+int oaktimeline_workarea_reset(int *in_num, int *in_den, int *out_num,
+							   int *out_den);
+
+/**
+ * @brief Load/save through oakcommon XML handles. The reader must be
+ * positioned on the "workarea" element.
+ */
+int oaktimeline_workarea_load(OakTimelineWorkArea *w, OakXmlReader reader);
+int oaktimeline_workarea_save(const OakTimelineWorkArea *w,
+							  OakXmlWriter writer);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif //OAK_EDITOR_TIMELINE_WORKAREA_H