feat(engine): clip move, clip effect_input, mandatory static FFmpeg

- oakengine_sequence_move_clip implemented for real (oaktimeline
  TrackMoveBlockCommand; fixes the graph-ownership/gap-anchor/ripple
  trim bugs the stub was hiding); same-track via the frozen C ABI,
  cross-track supported by the module command
- oaknode clip blocks now declare a tex_in texture input and set
  effect_input to it, so timeline clips can host effect chains; facade
  test covers effect insert/remove on a real clip
- oakffmpeg-link: FFMPEG_DIR is now mandatory with a clear panic (a
  Homebrew upgrade left the system ffmpeg .pc pointing at a deleted
  dav1d Cellar path, breaking links); reads a git-ignored workspace
  .env for IDEs that cannot inject env vars (RustRover); links the C++
  stdlib for C++ codec libs (svt-av1)
- oakengine re-exports oaknode so tests share one crate instance;
  it_node uses the direct instance's value type where it calls the
  module FFI (the --workspace dev-dependency feature split builds
  oaknode twice)

crates/oaknode/src/sequence.rs

@@ -72,8 +72,8 @@ impl SequenceBehavior {
 	/// `ViewerOutput::set_default_parameters()`; the config lookups use
 	/// oakcommon's defaults when the config module is absent).
 	pub fn set_default_parameters(&mut self) {
-		let width = crate::bridge::common::config_get_int("DefaultSequenceWidth", "", 1920)
-			.unwrap_or(1920);
+		let width =
+			crate::bridge::common::config_get_int("DefaultSequenceWidth", "", 1920).unwrap_or(1920);
 		let height = crate::bridge::common::config_get_int("DefaultSequenceHeight", "", 1080)
 			.unwrap_or(1080);
 		let sample_rate =
@@ -100,7 +100,14 @@ impl SequenceBehavior {
 
 	/// Recompute the cached lengths from the track lists (C++
 	/// `ViewerOutput::verify_length()`).
-	pub fn verify_length(&mut self, lengths: (oakcore_rs::Rational, oakcore_rs::Rational, oakcore_rs::Rational)) {
+	pub fn verify_length(
+		&mut self,
+		lengths: (
+			oakcore_rs::Rational,
+			oakcore_rs::Rational,
+			oakcore_rs::Rational,
+		),
+	) {
 		let (video, audio, overall) = lengths;
 		self.last_length = overall;
 		let _ = (video, audio);