Minimal per-user, per-scope view-preference store for Manufacturing's admin list pages — currently the Machines index's saved columns and active filters (see PhoenixKitManufacturing.ColumnConfig / Web.ColumnManagement).

Core owns the module's tables now (see PhoenixKit.Migrations.Postgres.V144); a standalone preferences table would need its own core PR. Instead this module stores a %{"columns" => [...], "active_filters" => [...]}-shaped map as a JSON-encoded blob in phoenix_kit_settings (core's flat key-value table), one row per (scope, user_uuid) pair, keyed "manufacturing_view_config:<scope>:<user_uuid>".

This is a 1:1 adaptation of PhoenixKitWarehouse.ViewConfigs — same trade-off applies: phoenix_kit_settings has no secondary index on "all rows for this user", which is fine at this module's scale (currently one scope — manufacturing_machines — times however many users actually customize columns) but is not a pattern to reach for at higher fan-out.