fix: address reviewer feedback — rename scroll field to bool, relocate static, drop env var

- Rename `ui_scroll_tick_count: u64` → `should_text_scroll: bool` across all 33
  call sites; `on_ui_scroll_tick` now assigns true/false instead of 0/1
- Remove two now-redundant comments from `test_on_ui_scroll_tick`
- Move `WHITESPACE_RE` static declaration below module imports in network/mod.rs
- Remove `MANAGARR_TICK_RATE_MS` env var and its parsing helpers; `recv()`-based
  blocking already brings idle CPU to near-0, and tuning tick rate silently
  stretches the poll cadence — keep `DEFAULT_TICK_RATE_MS` const only

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C3FpbniZme9mJqgFkMVowz

src/ui/radarr_ui/downloads/mod.rs

@@ -87,7 +87,7 @@ fn draw_downloads(f: &mut Frame<'_>, app: &mut App<'_>, area: Rect) {
       output_path.as_ref().unwrap().scroll_left_or_reset(
         get_width_from_percentage(area, 18),
         current_selection == *download_record,
-        app.ui_scroll_tick_count == 0,
+        app.should_text_scroll,
       );
     }