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/oaktask/src/customcache.rs

@@ -102,7 +102,10 @@ impl CustomCacheTask {
 	/// Create a cache-fill task with the given sequence name. The cancel
 	/// hook that wakes the parked thread is installed on the base task.
 	pub fn new(sequence_name: &str) -> CustomCacheTask {
-		let base = Task::new(&format!("Caching custom range for \"{sequence_name}\""), CHandle::null());
+		let base = Task::new(
+			&format!("Caching custom range for \"{sequence_name}\""),
+			CHandle::null(),
+		);
 		let state = Arc::new(CustomCacheState {
 			cancelled_through_finish: Mutex::new(false),
 			wait: Condvar::new(),
@@ -115,7 +118,8 @@ impl CustomCacheTask {
 			state,
 		};
 		let hook_state = task.state.clone();
-		task.base.set_cancel_event(Box::new(move || hook_state.cancel_event()));
+		task.base
+			.set_cancel_event(Box::new(move || hook_state.cancel_event()));
 		task
 	}