[FOWEPJF255]

What and why

Document that a matching Dictionary_ID does not verify dictionary contents, and recommend including the optional Content_Checksum for dictionary-compressed frames. Clarify that checksums are partial integrity checks: decoders may ignore them, and they do not authenticate a dictionary.

Related to #4845. This documents a mitigation and does not change format behavior.

Checklist

• I searched open pull requests and issues; this problem is not already being addressed.
• I stated below whether AI or other automated tools were used.
• Bug fix reproducer/test: not applicable (documentation change).
• Performance numbers: not applicable (documentation change).

Tools used

AI assistant: reviewed the issue and drafted the documentation wording. I checked the technical claims against the format documentation and CLI defaults, reviewed the generated man-page diff, and ran git diff --check plus strict UTF-8 decoding.