Read one datapoint's value from a company's profile

The read behind the answer page's "use values from your company profile" pre-fill: for one datapoint, what the company already has stored. Called once per datapoint-bound question, so it is a single-value lookup rather than a batch. dataPointId is a datapoint slug (official_name, vat_id), resolved through the datapoint library to the key that addresses the profile blob — an unrecognised slug answers 404 data_point_not_found. The profile is read from the caller's point of view: the datapoint's owning company is the path's companyId, but the profile must have been recorded by the caller's company, so a company with no such profile answers 404 company_not_found even when the company itself exists. That is the tenancy boundary, and it is a 404 rather than a 403 so it cannot be used to probe which companies exist. value is the stored blob passed through verbatim — shape depends on the datapoint's answer type, commonly {value, unit, year} — or null when no profile carries the key, which callers treat as nothing to pre-fill. The value is not restricted to the ABOUT profile: many datapoints are stored under other profile types (OTHER_IDS, OPERATIONAL_METRICS), and when the same key appears under more than one, ABOUT wins.