V108: Add position columns for drag-and-drop reordering on three list surfaces.

Three independent admin lists previously sat in insertion order (latest first or alphabetical) with no user-driven order:

• phoenix_kit_entities — the entity-definitions list at /admin/entities
• phoenix_kit_cat_catalogues — the catalogues index at /admin/catalogue
• phoenix_kit_cat_items — items shown on a catalogue's detail page and inside categories

Categories and smart-catalogue rules already carry their own position columns (V87 and V102 respectively), so they're untouched here. The phoenix_kit_entity_data table got its position column in V81 along with a (entity_uuid, position) composite index for the manual-sort query, so it's also already covered.

Up

Adds a nullable position integer to each of the three tables with a default of 0. New rows get 0; the LV reorder handlers re-index the visible group to 1..N on the first user drag, so the default is only ever observed transiently.

No indexes on the three new position columns themselves — entity / catalogue / item-per-catalogue lists are small (≤ a few hundred rows) and have other indexed scope filters; a position-only btree would burn write amplification for no real read win.

Down

Drops the three columns. Lossy — any user-set ordering is discarded.