docs(ords): correct file upload/download skill guidance

[Fm0007]

Summary

This PR corrects the ORDS file upload/download skill so the guidance matches current ORDS behavior. It fixes incorrect payload handling, replaces outdated multipart guidance, reworks the download examples around source_type_media, and updates the large-file and reference sections.

What changed

• Replaced the raw upload example so :body is copied once into a local BLOB and then reused safely.
• Added explicit guidance that :body and :body_text should be dereferenced only once unless first copied to a local variable.
• Reworked the multipart upload section to use current ORDS support with :body_json, ORDS.BODY_FILE_COUNT, and ORDS.GET_BODY_FILE.
• Removed the older multipart guidance that implied custom multipart parsing or APEX was required.
• Replaced the GET download pattern so it uses ORDS.source_type_media instead of source_type_plsql.
• Updated the media examples to use the documented shape: media type first, representation second.
• Removed the invalid PL/SQL download example that attempted chunked streaming with WPG_DOCLOAD.DOWNLOAD_FILE and RAW.
• Reworked the generated-download example so transformation happens behind source_type_media.
• Updated the large-file section to recommend ORDS media streaming instead of manual chunking.
• Removed the misleading misc.pagination.maxRows configuration example from the large-upload guidance.
• Updated best practices and common mistakes to reflect the corrected payload-handling rules.
• Updated the ORDS references to current 25.4 documentation and corrected the Developer’s Guide chapter link.

Validation

• Reviewed the updated skill for consistency and structure.
• Confirmed the upload example no longer dereferences :body multiple times.
• Confirmed the multipart section now documents current ORDS multipart handling.
• Confirmed GET download examples no longer use source_type_plsql.
• Confirmed the source_type_media examples now follow the documented query pattern.
• Confirmed the large-upload section no longer suggests pagination config as a request-size setting.
• Confirmed the ORDS Developer’s Guide source link now points to the valid developing-REST-applications.html chapter.
• Re-reviewed the final skill and found no remaining factual issues in the documentation.

Notes

• This is a skills/documentation change only.
• The review validated the guidance against current Oracle documentation; the sample handlers were executed against a live ORDS instance.