feat(views): saved-views store and API

Add a saved_views table (page images|library, trimmed 1-100 character
name, whitelisted JSON state of at most 4 KB, position, timestamps)
installed through the same validated-savepoint migration as image
favorites. It is optional in old backups and required in a migrated
restore stage; restore rejects a tampered definition, extra indexes and
any row that would fail write validation.

Routes under /prompt_manager/saved-views: GET lists views by position,
POST {page,name,state} returns 201 {success, view}, PATCH /{id} {name}
renames and DELETE /{id} removes, both 404 for an unknown id. The state
must hold exactly the page's toolbar and Refine-this-view keys (Images:
q, category, sort, source, folder, media, tags; Library: q, category,
sort, tags) with their types and sort/media values; anything else is a
400.

Refs #249

database/operations.py

@@ -12,6 +12,7 @@ from .models import PromptModel, normalize_image_path, utc_now_iso
 from .pairs import PairDependencyError, PairOperations
 from .library import LibraryOperations, titled
 from .image_favorites import ImageFavoriteOperations
+from .saved_views import SavedViewOperations
 from .library_commands import LibraryCommandOperations
 from .vocabulary import VocabularyOperations
 from .execution_history import ExecutionHistoryOperations
@@ -306,6 +307,7 @@ class PromptDatabase(
     ExecutionOutputOperations,
     HistoryReadOperations,
     ImageFavoriteOperations,
+    SavedViewOperations,
 ):
     """Database operations class for managing prompts."""