Fix: use 'refreshing' reactive to avoid Textual built-in loading dots

Widget.loading is a Textual built-in reactive that swaps the widget for the
default dots spinner. Our dashboard used the same name, so setting it True
activated the built-in indicator (dots) instead of the dog loader. Renamed
to 'refreshing' and assert app.screen.loading stays False in tests.

src/selectel_ml_tui/ui/app.py

@@ -134,7 +134,7 @@ class DashboardScreen(Screen[Any]):
     ]
 
     data = reactive(DashboardData())
-    loading = reactive(False)
+    refreshing = reactive(False)
 
     def __init__(
         self,
@@ -169,22 +169,22 @@ class DashboardScreen(Screen[Any]):
 
     @work(exclusive=True, group="refresh")
     async def _refresh(self) -> None:
-        self.loading = True
+        self.refreshing = True
         try:
             self.data = await self._service.refresh()
         except Exception as exc:  # noqa: BLE001 - показываем toast при ошибке
             self.notify(f"Ошибка обновления: {exc}", severity="error")
         finally:
-            self.loading = False
+            self.refreshing = False
 
-    def watch_loading(self, loading: bool) -> None:
+    def watch_refreshing(self, refreshing: bool) -> None:
         """Показать/скрыть собачку и строку прогресса при обновлении."""
         try:
             loader = self.query_one("#dog-loader", DogLoader)
             line = self.query_one("#progress-line", Static)
         except NoMatches:  # watcher может сработать до монтирования детей
             return
-        if loading:
+        if refreshing:
             loader.add_class("visible")
             loader.start()
             line.update("[b]🐕 Собачка обновляет статистику…[/]")

tests/test_tui.py

@@ -317,9 +317,12 @@ async def test_dog_loader_hidden_when_idle(tmp_path) -> None:
         await pilot.pause()
         loader = app.screen.query_one("#dog-loader", DogLoader)
         assert not loader.has_class("visible")
+        assert loader.display is False
         assert not loader.running
         line = app.screen.query_one("#progress-line", Static)
         assert str(line.render()) == ""
+        # встроенный loading Textual не должен активироваться (иначе — точки)
+        assert app.screen.loading is False
 
 
 async def test_dog_loader_shown_during_refresh(tmp_path) -> None:
@@ -339,13 +342,16 @@ async def test_dog_loader_shown_during_refresh(tmp_path) -> None:
         await pilot.pause()
         loader = app.screen.query_one("#dog-loader", DogLoader)
         assert loader.has_class("visible")
+        assert loader.display is True
         assert loader.running
         line = app.screen.query_one("#progress-line", Static)
         assert "обновляет статистику" in str(line.render())
+        assert app.screen.loading is False
 
         release.set()
         await pilot.pause(0.1)
         assert not loader.has_class("visible")
+        assert loader.display is False
         assert not loader.running
         assert str(line.render()) == ""