Fixed the scroll direction bug where PageUp/PageDown were inverted:
- page_up now scrolls UP (back in time) with positive delta (+10)
- page_down now scrolls DOWN (forward in time) with negative delta (-10)
- Mouse wheel up/down also fixed with same logic (+3/-3)
The scroll logic in scroll_output() was correct (positive = scroll up),
but the key handlers in both main.py and pipeline_runner.py had
the signs inverted.