Fix scroll direction inversion in REPL

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.

engine/app/main.py

@@ -576,9 +576,13 @@ def run_pipeline_mode_direct():
                     elif key == "down":
                         repl_effect.navigate_history(1)
                     elif key == "page_up":
-                        repl_effect.scroll_output(-10)  # Scroll up 10 lines
+                        repl_effect.scroll_output(
+                            10
+                        )  # Positive = scroll UP (back in time)
                     elif key == "page_down":
-                        repl_effect.scroll_output(10)  # Scroll down 10 lines
+                        repl_effect.scroll_output(
+                            -10
+                        )  # Negative = scroll DOWN (forward in time)
                     elif key == "backspace":
                         repl_effect.backspace()
                     elif key.startswith("mouse:"):
@@ -587,9 +591,9 @@ def run_pipeline_mode_direct():
                         if len(parts) >= 2:
                             button = int(parts[1])
                             if button == 64:  # Wheel up
-                                repl_effect.scroll_output(-3)  # Scroll up 3 lines
+                                repl_effect.scroll_output(3)  # Positive = scroll UP
                             elif button == 65:  # Wheel down
-                                repl_effect.scroll_output(3)  # Scroll down 3 lines
+                                repl_effect.scroll_output(-3)  # Negative = scroll DOWN
                     elif len(key) == 1:
                         repl_effect.append_to_command(key)
             # --- End REPL Input Handling ---