Parse a GCS CSV file into JSON headers and rows

Retrieves a CSV file from the configured Google Cloud Storage bucket by its object path, parses it with the server-side CSV parser, and returns a FileParserResponse. The response has two fields: headers, an ordered array of column-name strings, and rows, an array of objects keyed by column name whose values are strings or null. Empty cells in the source CSV are normalized to null. Use this endpoint when you need the CSV as machine-readable structured data, such as rendering rows in a table or validating column presence before processing; use GET /file/download instead when you need the raw file bytes. Supply the path query parameter with the GCS object name (for example, imports/my-file.csv) and a valid JWT. On success returns HTTP 200 with the parsed JSON body.