#2959 data query: binary content lacks contentEncoding/base64 parity with data get

Gap

swamp data get returns content without loss: UTF-8 text when the stored bytes are valid UTF-8, otherwise base64, with a contentEncoding field of utf-8 or base64 (content_encoding.ts encodeContent). It is unverified whether swamp data query --select content (and the default content field in query results) handles binary content the same way.

Expected

Verify and, if needed, make data query return binary content losslessly with the same contentEncoding convention, in both log and --json output.

Context: swamp data get is being deprecated in favor of swamp data query (follow-up to swamp-club#2948, where data get --workflow silently returns an arbitrary step's data when several steps share a data name). This closes one gap that data query has compared with data get.

Update: binary content is not loaded at all

In data_record_mapper.ts, content is loaded only for text, JSON and YAML content types (isTextContentType). Binary items (images, archives) therefore have no content in data query results, so there is no query equivalent of data get --json returning base64 bytes. The swamp skill still documents data get for downloading a binary item (data/reference.md, data/references/fields.md) until this is fixed.