Resolve a prompt to the primitive values it selects, across every table.

Returns filters, not features. The client already holds the county's tiles, so a value set is all it needs to repaint — which is why this can be a single small request on the interactive path instead of a re-render.

Unmatched prompts return no filters rather than a best guess: a preview that lights something up for "asdfghjkl" is worse than one that stays dark.