Favorites bulk context menu, slideshow state buttons

- Add multi-select right-click menu in favorites (save all, unsave
  all, move all, unfavorite all)
- Slideshow toolbar buttons show post state: Favorite/Unfavorite,
  Save enabled/disabled, Unsave enabled/disabled
- State updates after every favorite/save/unsave action

booru_viewer/gui/app.py

@@ -740,6 +740,23 @@ class BooruApp(QMainWindow):
         if self._fullscreen_window and self._fullscreen_window.isVisible():
             self._preview._video_player.stop()
             self._fullscreen_window.set_media(path, info)
+            self._update_fullscreen_state()
+
+    def _update_fullscreen_state(self) -> None:
+        """Update slideshow button states for the current post."""
+        if not self._fullscreen_window:
+            return
+        idx = self._grid.selected_index
+        site_id = self._site_combo.currentData()
+        if 0 <= idx < len(self._posts) and site_id:
+            post = self._posts[idx]
+            favorited = self._db.is_favorited(site_id, post.id)
+            saved = False
+            if 0 <= idx < len(self._grid._thumbs):
+                saved = self._grid._thumbs[idx]._saved_locally
+            self._fullscreen_window.update_state(favorited, saved)
+        else:
+            self._fullscreen_window.update_state(False, False)
 
     def _on_image_done(self, path: str, info: str) -> None:
         self._dl_progress.hide()
@@ -841,6 +858,7 @@ class BooruApp(QMainWindow):
         idx = self._grid.selected_index
         if 0 <= idx < len(self._posts):
             self._toggle_favorite(idx)
+            self._update_fullscreen_state()
 
     def _save_from_preview(self, folder: str) -> None:
         idx = self._grid.selected_index
@@ -849,6 +867,7 @@ class BooruApp(QMainWindow):
             if folder and folder not in self._db.get_folders():
                 self._db.add_folder(folder)
             self._save_to_library(self._posts[idx], target)
+            self._update_fullscreen_state()
 
     def _unsave_from_preview(self) -> None:
         idx = self._grid.selected_index
@@ -869,6 +888,7 @@ class BooruApp(QMainWindow):
                     self._grid._thumbs[idx].set_saved_locally(False)
             else:
                 self._status.showMessage(f"#{post.id} not in library")
+            self._update_fullscreen_state()
 
     def _open_fullscreen_preview(self) -> None:
         path = self._preview._current_path
@@ -885,6 +905,7 @@ class BooruApp(QMainWindow):
         self._fullscreen_window.unsave_requested.connect(self._unsave_from_preview)
         self._fullscreen_window.destroyed.connect(self._on_fullscreen_closed)
         self._fullscreen_window.set_media(path, self._preview._info_label.text())
+        self._update_fullscreen_state()
 
     def _on_fullscreen_closed(self) -> None:
         self._fullscreen_window = None

booru_viewer/gui/favorites.py

@@ -86,6 +86,7 @@ class FavoritesView(QWidget):
         self._grid.post_selected.connect(self._on_selected)
         self._grid.post_activated.connect(self._on_activated)
         self._grid.context_requested.connect(self._on_context_menu)
+        self._grid.multi_context_requested.connect(self._on_multi_context_menu)
         layout.addWidget(self._grid)
 
     def _refresh_folders(self) -> None:
@@ -299,3 +300,57 @@ class FavoritesView(QWidget):
             delete_from_library(fav.post_id, fav.folder)
             self._db.remove_favorite(fav.site_id, fav.post_id)
             self.refresh()
+
+    def _on_multi_context_menu(self, indices: list, pos) -> None:
+        favs = [self._favorites[i] for i in indices if 0 <= i < len(self._favorites)]
+        if not favs:
+            return
+
+        menu = QMenu(self)
+        save_all = menu.addAction(f"Save All ({len(favs)}) to Library")
+        unsave_all = menu.addAction(f"Unsave All ({len(favs)}) from Library")
+        menu.addSeparator()
+
+        move_menu = menu.addMenu(f"Move All ({len(favs)}) to Folder")
+        move_none = move_menu.addAction("Unfiled")
+        move_menu.addSeparator()
+        folder_actions = {}
+        for folder in self._db.get_folders():
+            a = move_menu.addAction(folder)
+            folder_actions[id(a)] = folder
+
+        menu.addSeparator()
+        unfav_all = menu.addAction(f"Unfavorite All ({len(favs)})")
+
+        action = menu.exec(pos)
+        if not action:
+            return
+
+        if action == save_all:
+            for fav in favs:
+                if fav.folder:
+                    self._copy_to_library(fav, fav.folder)
+                else:
+                    self._copy_to_library_unsorted(fav)
+            self.refresh()
+        elif action == unsave_all:
+            from ..core.cache import delete_from_library
+            for fav in favs:
+                delete_from_library(fav.post_id, fav.folder)
+            self.refresh()
+        elif action == move_none:
+            for fav in favs:
+                self._db.move_favorite_to_folder(fav.id, None)
+            self.refresh()
+        elif id(action) in folder_actions:
+            folder_name = folder_actions[id(action)]
+            for fav in favs:
+                self._db.move_favorite_to_folder(fav.id, folder_name)
+                self._copy_to_library(fav, folder_name)
+            self.refresh()
+        elif action == unfav_all:
+            from ..core.cache import delete_from_library
+            for fav in favs:
+                delete_from_library(fav.post_id, fav.folder)
+                self._db.remove_favorite(fav.site_id, fav.post_id)
+            self.refresh()

booru_viewer/gui/preview.py

@@ -83,6 +83,12 @@ class FullscreenPreview(QMainWindow):
         QApplication.instance().installEventFilter(self)
         self.showFullScreen()
 
+    def update_state(self, favorited: bool, saved: bool) -> None:
+        self._fav_btn.setText("Unfavorite" if favorited else "Favorite")
+        self._fav_btn.setFixedWidth(90 if favorited else 80)
+        self._save_btn.setEnabled(not saved)
+        self._unsave_btn.setEnabled(saved)
+
     def set_media(self, path: str, info: str = "") -> None:
         self._info_label.setText(info)
         ext = Path(path).suffix.lower()