v1.6.0 — control:"choices" record picker

Adds control: "choices" — a record picker for repeater fields whose option list the HOST SITE supplies (core ships none), the same contract as control: "icon".

A field opts in with {"control": "choices", "source": "<key>"} and the site localises window.framixBlocksChoices.<key> = [{value, label, description, thumb}] onto the framix-blocks-repeater-control handle.

• Stores the plain value string, so switching an existing free-text field to this control rewrites no content.
• A stored value missing from the list is kept and reported, never blanked or snapped to the first option.
• An unregistered source degrades to the plain text input, so blocks using it still work on sites that registered nothing.

Sites using the control need this version: on an older core the validator rejects it and the loader SKIPS the whole block.