refactor: drop new_offset alias in _FullscreenPeek.scroll_down

The local was assigned immediately to `self._offset`, then the
follow-mode check re-read it as `new_offset == 0`.  Reading
`self._offset` directly after assignment has identical semantics
— the alias added no value.

Sibling `scroll_up` keeps its local because it compares the new
value against the old one *before* the assignment (to conditionally
disable auto-scroll), which requires two distinct values.
`scroll_down` has no such comparison, so the alias is dead.

Same shape as ef176bf (`line_count`) and 134078d (`name_col`).

Co-authored-by: Ralphify <noreply@ralphify.co>

Author: 2 people

src/ralphify/_console_emitter.py

@@ -763,9 +763,8 @@ def scroll_up(self, lines: int = 1) -> None:
 
     def scroll_down(self, lines: int = 1) -> None:
         """Scroll toward newer lines (offset shrinks)."""
-        new_offset = max(0, self._offset - lines)
-        self._offset = new_offset
-        if new_offset == 0:
+        self._offset = max(0, self._offset - lines)
+        if self._offset == 0:
             self._auto_scroll = True
 
     def scroll_to_top(self) -> None: