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

src/node/c_api/node.cpp

@@ -32,6 +32,8 @@
 
 #include "output/viewer/viewer.h"
 
+#include "project/footage/footage.h"
+
 #include "valueconvert.h"
 
 namespace
@@ -1332,3 +1334,23 @@ int oaknode_viewer_set_audio_params(OakNodeNode *viewer,
 		return OAKNODE_E_FAILED;
 	}
 }
+
+int oaknode_node_find_input_footage(const OakNodeNode *node,
+									OakNodeFootage **out)
+{
+	if (!node || !out) {
+		return OAKNODE_E_INVALID;
+	}
+
+	*out = NULL;
+	try {
+		std::vector<olive::Footage *> found =
+			to_node(node)->find_input_nodes<olive::Footage>();
+		if (!found.empty()) {
+			*out = reinterpret_cast<OakNodeFootage *>(found.front());
+		}
+		return OAKNODE_OK;
+	} catch (...) {
+		return OAKNODE_E_FAILED;
+	}
+}

src/node/c_api/sequence.cpp

@@ -323,3 +323,17 @@ OakNodeNode *oaknode_sequence_as_node(OakNodeSequence *sequence)
 {
 	return reinterpret_cast<OakNodeNode *>(sequence);
 }
+
+int oaknode_sequence_set_default_parameters(OakNodeSequence *sequence)
+{
+	if (!sequence) {
+		return OAKNODE_E_INVALID;
+	}
+
+	try {
+		impl(sequence)->set_default_parameters();
+		return OAKNODE_OK;
+	} catch (...) {
+		return OAKNODE_E_FAILED;
+	}
+}