Add bulk edit for row properties

## Goal

Editing one property across many rows is a routine task ("set Status to Done on these five"). Today you do it row by row. Add a bulk-edit option from the row selection.

## Scope

* From a multi-row selection, a Bulk edit action opens a modal.
* The modal lets you pick one editable field and either set a value or clear it.
* Editable: any field that holds a stored value, including relations.
* For multi-value fields (multiselect, relation), the new value replaces the existing one on each row.
* Result feedback: a summary of how many rows updated and how many failed.

## Out of scope

* Title, formula, and rollup. Title is each row's identity; formula and rollup are computed, no value to set.
* Conditional bulk edits, e.g. "set Status only if currently In Progress".

## Acceptance criteria

* From a multi-row selection, Bulk edit opens a modal.
* Picking a field and a value updates all selected rows; the result shows success and failure counts.
* The clear-value toggle sets the field to empty on every selected row.
* Multi-value fields replace, not merge.

Start at the row-selection entry point and trace the existing property-edit and row-update flows before designing the Bulk edit action and modal. Verify behavior against the stated acceptance criteria: editable stored fields excluding title, formula, and rollup; set or clear values; replace multi-value fields; and report updated and failed row counts.

Written by the indexing model from the issue text.