Returns address completion previews for a partial street address, suitable for populating an autocomplete dropdown without consuming a lookup per keystroke.

Each result contains a partial address preview (street, city, and — for non-US addresses — only the first 3 digits of the postal code, to avoid revealing the full code before a lookup is charged).

• Does not consume a lookup.
• Use POST /completions to resolve a full address once the user selects a result.