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

py/api/__init__.py

@@ -25,6 +25,7 @@ from .prompts import PromptRoutesMixin
 from .pairs import PairRoutesMixin
 from .library import LibraryRoutesMixin
 from .vocabulary import VocabularyRoutesMixin
+from .saved_views import SavedViewRoutesMixin
 from .history import HistoryRoutesMixin
 from .images import ImageRoutesMixin
 from .admin import AdminRoutesMixin
@@ -248,6 +249,7 @@ class PromptManagerAPI(
     PairRoutesMixin,
     LibraryRoutesMixin,
     VocabularyRoutesMixin,
+    SavedViewRoutesMixin,
     HistoryRoutesMixin,
     PromptRoutesMixin,
     ImageRoutesMixin,
@@ -432,6 +434,7 @@ class PromptManagerAPI(
         self._register_pair_routes(routes)
         self._register_library_routes(routes)
         self._register_vocabulary_routes(routes)
+        self._register_saved_view_routes(routes)
         self._register_history_routes(routes)
         self._register_prompt_routes(routes)
         self._register_image_routes(routes)