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/oakengine/include/timeline/edit.h

@@ -61,6 +61,18 @@ OakUndoCommand oaktimeline_place_block_command(OakNodeTrackList list,
 OakUndoCommand oaktimeline_replace_block_with_gap_command(
 	OakNodeTrack track, OakNodeBlock block);
 
+/**
+ * @brief The capi's move-clip assembly: gap the block's old spot and place
+ * it at `in` on `track_index` of `list` as ONE undoable entry
+ * (olive::TrackReplaceBlockWithGapCommand + olive::TrackPlaceBlockCommand
+ * inside a MultiUndoCommand).
+ */
+OakUndoCommand oaktimeline_move_block_command(OakNodeTrackList list,
+												int track_index,
+												OakNodeBlock block,
+												int64_t in_num,
+												int64_t in_den);
+
 /**
  * @brief olive::BlockTrimCommand. `mode` is an OakTimelineMovementMode
  * value (k_trim_in / k_trim_out).