feat(api): consolidate user profile update endpoints

Add delete_user, reset_user_password, and update_user endpoints to replace
individual update operations. Update database schema to include deleted_at
column for soft deletion. Add DeleteUser, ResetUserPassword, and
UpdateUserAdmin queries. Update Querier with new methods for user management.

database/schema/schema.sql

@@ -902,14 +902,8 @@ CREATE INDEX IF NOT EXISTS idx_collection_items_media ON collection_items(media_
 CREATE INDEX IF NOT EXISTS idx_collection_items_excluded ON collection_items(collection_id, excluded)
     WHERE excluded = true;
 
--- Insert 4 system collections (pre-seeded defaults)
--- These are user_id NULL to indicate system ownership
-INSERT INTO collections (user_id, name, description, icon, color, show_on_dashboard, query_type, priority, is_system_collection, auto_assign_rules) VALUES
-(NULL, 'continue-reading', 'Books you''re currently reading (0 < progress < 1)', '📖', '#7aa2f7', true, 'continue-reading', 1, true, 'null'),
-(NULL, 'recently-added', 'Newly added items to this library', '🆕', '#9ece6a', true, 'recently-added', 2, true, 'null'),
-(NULL, 'recently-read', 'Books you''ve finished (progress >= 1)', '✅', '#e0af68', true, 'recently-read', 3, true, 'null'),
-(NULL, 'not-started', 'Books you haven''t read yet (progress = 0 or no record)', '📕', '#f7768e', true, 'not-started', 4, true, 'null')
-ON CONFLICT (user_id, name) DO NOTHING;
+-- System collections are now created per-user upon registration
+-- See CreateDefaultCollectionsForUser in auth.go
 
 -- Create device_shelf_mappings table (map Bookhoard collections to device-specific shelf names)
 CREATE TABLE IF NOT EXISTS device_shelf_mappings (