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/models.py

@@ -17,6 +17,7 @@ from typing import Optional, Set, Tuple
 
 from .library_schema import library_schema_error, migrate_library_state
 from .image_favorites import image_favorites_schema_error, migrate_image_favorites
+from .saved_views import migrate_saved_views, saved_views_schema_error
 from .execution_history_schema import (
     history_schema_error,
     migrate_execution_history,
@@ -300,6 +301,7 @@ class PromptModel:
         migrate_execution_history(conn)
         migrate_library_state(conn)
         migrate_image_favorites(conn)
+        migrate_saved_views(conn)
 
     def _migrate_prompt_pairs(self, conn: sqlite3.Connection) -> None:
         conn.execute("SAVEPOINT prompt_pair_schema")
@@ -1019,8 +1021,9 @@ class PromptModel:
         Args:
             path: File to inspect
             require_library_state: Also require the tables every current
-                database has (Library state and image favorites), as a
-                migrated restore stage must; old backups may lack them.
+                database has (Library state, image favorites and saved
+                views), as a migrated restore stage must; old backups may
+                lack them.
 
         Returns:
             (ok, reason): reason is "ok" when the file is acceptable, otherwise
@@ -1080,6 +1083,11 @@ class PromptModel:
             )
             if favorites_error:
                 return False, favorites_error
+            views_error = saved_views_schema_error(
+                conn, allow_missing=not require_library_state
+            )
+            if views_error:
+                return False, views_error
             return True, "ok"
         except sqlite3.Error as e:
             return False, f"Invalid SQLite database: {e}"