Scroll tilt flips pages without auto-selecting first post

Separate page_forward/page_back signals from nav boundary signals
so tilt just changes page, doesn't trigger post preview.

booru_viewer/gui/app.py

@@ -328,6 +328,8 @@ class BooruApp(QMainWindow):
         self._grid.multi_context_requested.connect(self._on_multi_context_menu)
         self._grid.nav_past_end.connect(self._on_nav_past_end)
         self._grid.nav_before_start.connect(self._on_nav_before_start)
+        self._grid.page_forward.connect(self._next_page)
+        self._grid.page_back.connect(self._prev_page)
         self._stack.addWidget(self._grid)
 
         self._favorites_view = FavoritesView(self._db)

booru_viewer/gui/grid.py

@@ -222,6 +222,8 @@ class ThumbnailGrid(QScrollArea):
     reached_top = Signal()     # emitted when scrolled to the top
     nav_past_end = Signal()    # keyboard nav past last post
     nav_before_start = Signal()  # keyboard nav before first post
+    page_forward = Signal()    # scroll tilt right
+    page_back = Signal()       # scroll tilt left
 
     def __init__(self, parent: QWidget | None = None) -> None:
         super().__init__(parent)
@@ -402,9 +404,9 @@ class ThumbnailGrid(QScrollArea):
     def wheelEvent(self, event: QWheelEvent) -> None:
         delta = event.angleDelta().x()
         if delta > 30:
-            self.nav_before_start.emit()
+            self.page_back.emit()
         elif delta < -30:
-            self.nav_past_end.emit()
+            self.page_forward.emit()
         else:
             super().wheelEvent(event)