refactor(task): OTIO load/save tasks over oaknode/oaktimeline C ABIs

- LoadOTIOTask/SaveOTIOTask de-Qt'd: graph traversal and construction
  through oaknode C ABI (find_input_footage, sequence defaults, block
  factories, context positions), track creation through oaktimeline's
  add_track command; the OTIO import dialog becomes a facade callback
  (headless default: accept all)
- oaknode additions: find_input_footage, sequence_set_default_parameters
- USE_OTIO + otio-install libs wired into oaktask; OTIO dylibs copied
  next to liboaktask for @loader_path resolution
- OTIO round-trip test passes; build-oaktask 106/106 green

include/node/node.h

@@ -103,6 +103,9 @@ typedef struct OakNodeNode OakNodeNode;
 /* Re-declared here so node.h is self-contained; see node/project.h. */
 typedef struct OakNodeProject OakNodeProject;
 
+/* Re-declared here so node.h is self-contained; see node/footage.h. */
+typedef struct OakNodeFootage OakNodeFootage;
+
 /**
  * @brief Opaque borrowed handles to the timeline data owned by viewer
  * nodes (TimelineMarkerList / TimelineWorkArea in oaktimeline).
@@ -588,6 +591,14 @@ int oaknode_viewer_set_video_params(OakNodeNode *viewer,
 int oaknode_viewer_set_audio_params(OakNodeNode *viewer,
 									const OakAudioParams *params);
 
+/**
+ * @brief Find a footage node upstream of this node's inputs
+ *        (Node::find_input_nodes<Footage>(), first match). *out is a
+ *        borrowed handle or NULL when none.
+ */
+int oaknode_node_find_input_footage(const OakNodeNode *node,
+									OakNodeFootage **out);
+
 /**
  * @brief Create a command that removes a node from its graph together
  * with its exclusive dependencies and disconnects its edges

include/node/sequence.h

@@ -83,6 +83,12 @@ void oaknode_sequence_free(OakNodeSequence *sequence);
  * @param type One of OAKNODE_TRACK_TYPE_VIDEO / _AUDIO / _SUBTITLE.
  * @return OAKNODE_OK, OAKNODE_E_INVALID or OAKNODE_E_NOT_FOUND (bad type).
  */
+/**
+ * @brief Apply the default video/audio parameters
+ *        (ViewerOutput::set_default_parameters()).
+ */
+int oaknode_sequence_set_default_parameters(OakNodeSequence *sequence);
+
 /**
  * @brief Borrowed cast from a sequence handle to its node handle.
  * NULL for NULL.

include/task/project.h

@@ -70,6 +70,25 @@ int oaktask_import_invalid_count(OakTaskTask *t);
 int oaktask_import_invalid_at(OakTaskTask *t, int index, char *buf,
 							  int buf_size);
 
+/** @brief olive::LoadOTIOTask. */
+OakTaskTask *oaktask_create_project_load_otio(const char *filename);
+
+/** @brief Take the loaded project (ownership transfer). */
+OakNodeProject *oaktask_load_otio_take_project(OakTaskTask *t);
+
+/** @brief olive::SaveOTIOTask. */
+OakTaskTask *oaktask_create_project_save_otio(OakNodeProject *project,
+											  const char *filename);
+
+/**
+ * @brief OTIO import confirmation callback (facade concern; default
+ *        accepts everything). Return non-zero to accept.
+ */
+typedef int (*oaktask_otio_import_confirm_fn)(
+	const char *const *sequence_names, int count, void *userdata);
+void oaktask_load_otio_set_confirm_cb(oaktask_otio_import_confirm_fn fn,
+									  void *userdata);
+
 /** @brief olive::PreCacheTask. */
 OakTaskTask *oaktask_create_precache(OakNodeFootage *footage, int index,
 									 OakNodeSequence *sequence);