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/app/app_tests.rs

@@ -83,7 +83,7 @@ mod tests {
     assert_eq!(app.tick_until_poll, 400);
     assert_eq!(app.scroll_interval, Duration::from_millis(100));
     assert_eq!(app.tick_count, 0);
-    assert_eq!(app.ui_scroll_tick_count, 0);
+    assert!(!app.should_text_scroll);
     assert!(!app.is_loading);
     assert!(!app.is_routing);
     assert!(!app.should_refresh);
@@ -252,19 +252,16 @@ mod tests {
       ..App::default()
     };
 
-    // Zero interval: elapsed() >= scroll_interval is always true, so every
-    // call should signal "scroll now" (ui_scroll_tick_count == 0)
     app.on_ui_scroll_tick();
-    assert_eq!(app.ui_scroll_tick_count, 0);
+    assert!(app.should_text_scroll);
 
     app.on_ui_scroll_tick();
-    assert_eq!(app.ui_scroll_tick_count, 0);
+    assert!(app.should_text_scroll);
 
-    // Long interval with a fresh timestamp: should signal "not yet" (count == 1)
     app.scroll_interval = Duration::from_secs(60);
     app.last_scroll = Instant::now();
     app.on_ui_scroll_tick();
-    assert_eq!(app.ui_scroll_tick_count, 1);
+    assert!(!app.should_text_scroll);
   }
 
   #[tokio::test]