Implement collection item reordering with bulk operations and persistent HTML attributes

- Add bulk reorder API endpoint (PUT /api/collections/{id}/reorder) with atomic transactions
- Replace individual position updates with efficient bulk operations in frontend
- Implement unified ID generation and proper data-item-id injection during enhancement
- Fix collection item position persistence through content edit cycles
- Add optimistic UI with rollback capability for better user experience
- Update sqlc queries to include last_edited_by fields in position updates
- Remove obsolete data-content-type attributes and unify naming conventions

internal/db/postgresql/collection_items.sql.go

@@ -305,12 +305,13 @@ func (q *Queries) UpdateCollectionItem(ctx context.Context, arg UpdateCollection
 
 const updateCollectionItemPosition = `-- name: UpdateCollectionItemPosition :exec
 UPDATE collection_items 
-SET position = $1
-WHERE item_id = $2 AND collection_id = $3 AND site_id = $4
+SET position = $1, updated_at = CURRENT_TIMESTAMP, last_edited_by = $2
+WHERE item_id = $3 AND collection_id = $4 AND site_id = $5
 `
 
 type UpdateCollectionItemPositionParams struct {
 	Position     int32  `json:"position"`
+	LastEditedBy string `json:"last_edited_by"`
 	ItemID       string `json:"item_id"`
 	CollectionID string `json:"collection_id"`
 	SiteID       string `json:"site_id"`
@@ -319,6 +320,7 @@ type UpdateCollectionItemPositionParams struct {
 func (q *Queries) UpdateCollectionItemPosition(ctx context.Context, arg UpdateCollectionItemPositionParams) error {
 	_, err := q.db.ExecContext(ctx, updateCollectionItemPosition,
 		arg.Position,
+		arg.LastEditedBy,
 		arg.ItemID,
 		arg.CollectionID,
 		arg.SiteID,