refact[fluent/search]: format original file

[charlotte-nudibranches]

return formatted original file as a JSON object instead of just a string to allow easier access to data

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Note

Search result model update

• DocumentRecord.original_file now uses a structured OriginalFilePayload (with original_file_path, source_data_dock_id, source_filename).
• Added custom UnmarshalJSON to accept both a quoted JSON string and a direct JSON object for backward-compatible parsing.

Examples

• New runSearchExample demonstrates fluent search, selects original_file, executes the query, and prints S3 URL from original_file_path.
• Enabled runFluentAPIWithSelectExample and supporting helpers (handleResponse, splitColumns).
• main.go now invokes S3, SELECT, and Search examples.

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