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/oakcodec/src/task.rs

@@ -98,10 +98,8 @@ pub struct OakCodecTaskRequest {
 /// `oakcodec_task_submit_fn` — the extern-C submit callback typedef; see
 /// `include/codec/task.h`. Returns `OAKCODEC_OK` on accept, else a
 /// negative `OAKCODEC_E_*` code.
-pub type OakCodecTaskSubmitFn = unsafe extern "C" fn(
-	req: *const OakCodecTaskRequest,
-	userdata: *mut std::ffi::c_void,
-) -> i32;
+pub type OakCodecTaskSubmitFn =
+	unsafe extern "C" fn(req: *const OakCodecTaskRequest, userdata: *mut std::ffi::c_void) -> i32;
 
 /// One registered submit callback (extern-C from the host, or a crate
 /// Rust closure). Mirrors the C++ `g_task_cb`/`g_task_cb_userdata` pair.
@@ -175,9 +173,7 @@ pub fn task_submit_is_registered() -> bool {
 ///
 /// Returns `Ok(false)` when no callback is registered (nothing submitted),
 /// `Ok(true)` when accepted, or `Err` when the callback rejected it.
-pub fn submit_task(
-	req: &TaskRequest,
-) -> crate::error::Result<bool> {
+pub fn submit_task(req: &TaskRequest) -> crate::error::Result<bool> {
 	let g = TASK_SUBMIT.lock().unwrap();
 	match &*g {
 		SubmitCb::None => Ok(false),
@@ -203,7 +199,10 @@ pub fn submit_task(
 			if ret == OAKCODEC_OK {
 				Ok(true)
 			} else {
-				Err(Error::Failed(format!("task submit rejected (code {})", ret)))
+				Err(Error::Failed(format!(
+					"task submit rejected (code {})",
+					ret
+				)))
 			}
 		}
 		SubmitCb::Rust { cb, userdata } => {
@@ -301,7 +300,10 @@ mod tests {
 	#[test]
 	fn extern_cb_accept_returns_ok() {
 		let _g = REG_LOCK.lock().unwrap();
-		set_task_submit_cb_extern(Some(crate::conformmanager::test_util::accept_cb), std::ptr::null_mut());
+		set_task_submit_cb_extern(
+			Some(crate::conformmanager::test_util::accept_cb),
+			std::ptr::null_mut(),
+		);
 		let req = TaskRequest {
 			kind: TaskKind::Conform,
 			input_filename: "in.mp4",