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/nodes/polygon.rs

@@ -272,7 +272,10 @@ mod tests {
 	#[test]
 	fn input_names() {
 		let n = PolygonGenerator;
-		assert_eq!(n.input_name(super::super::generatorwithmerge::BASE_INPUT), "Base");
+		assert_eq!(
+			n.input_name(super::super::generatorwithmerge::BASE_INPUT),
+			"Base"
+		);
 		assert_eq!(n.input_name(POINTS_INPUT), "Points");
 		assert_eq!(n.input_name(COLOR_INPUT), "Color");
 	}
@@ -297,7 +300,10 @@ mod tests {
 			core.get_input(COLOR_INPUT).unwrap().default,
 			NodeValue::Color([1.0, 1.0, 1.0, 1.0])
 		);
-		assert_eq!(core.effect_input, super::super::generatorwithmerge::BASE_INPUT);
+		assert_eq!(
+			core.effect_input,
+			super::super::generatorwithmerge::BASE_INPUT
+		);
 		assert_ne!(core.flags & crate::node::flags::VIDEO_EFFECT, 0);
 	}