feat(images): Show removed images and Return to library (#498)

- GET /images/output?mode=workspace&removed=1 lists only files a removal
  mark hides; every workspace page carries removed_total.
- POST /images/removed/return {items | filter} starts a scan job,
  "Return images to the library": the marks that still hide their file
  go in one transaction, then exactly those files are scanned, so their
  prompt links come back from their metadata. Tags, categories,
  collections and favorites do not come back.
- The marks generation moves again after the commit, so a reader that
  cached the marks mid-transaction reloads them.
- Images: Show removed images (N) heading toggle (D162), Removed chips,
  a bar with only Return to library and Clear, Return to library in the
  side panel; the view is never saved or restored.

py/api/__init__.py

@@ -76,6 +76,7 @@ from .lora_integration import LoraIntegrationMixin
 from .lora_import_routes import LoraImportRoutesMixin
 from .image_categories import ImageCategoryRoutesMixin
 from .image_delete import ImageDeleteMixin
+from .image_return import ImageReturnMixin
 from .source_rescope import SourceRescopeMixin
 
 try:
@@ -346,6 +347,7 @@ class PromptManagerAPI(
     LoraImportRoutesMixin,
     ImageCategoryRoutesMixin,
     ImageDeleteMixin,
+    ImageReturnMixin,
     SourceRescopeMixin,
 ):
     """REST API handler for PromptManager operations and web interface.
@@ -724,6 +726,7 @@ class PromptManagerAPI(
         self._register_lora_import_routes(routes)
         self._register_image_category_routes(routes)
         self._register_image_delete_routes(routes)
+        self._register_image_return_routes(routes)
         self._register_rescope_routes(routes)
 
         # Register gzip compression middleware (once)