docs(vendor): the AppType template keeps a release-versioned note and decision history #2315

Is your feature request related to a problem? Please describe.
Two passes of BASE in pcapkit/vendor/reg/apptype/apptype.py read as history. Both are mirrored in the generated pcapkit/const/reg/apptype/apptype.py.

• The comment on TransportProtocol says: "Before 1.5.0 the class was an IntFlag with sctp at 4 and dccp at 8 …".
• TransportProtocol.get says: "… rather than from any name-miss policy. So there was no policy here to preserve".

#1872 ruled that the vendor templates and the generated files carry no version directives, and that a user-facing change note goes on the hand-written docs/source/pcapkit/const/*.rst page. The .. versionchanged:: 1.5.0 on docs/source/pcapkit/const/reg.rst already records the renumbering, so the template comment duplicates it in prose.

Describe the solution you'd like
Drop the "Before 1.5.0 …" sentence from the template comment, and add the bare-4-resolves-as-dccp hazard to the reg.rst note if it is wanted. Restate the get passage as current behaviour: a name miss raises EnumKeyError from the base. Change the template and the const file together, without re-crawling.

Describe alternatives you've considered
Keep the release-versioned note as a deliberate exception to #1872.

Additional context
#2175 reworded the change-relative prose in the same template and left these two passes.

Recommendation: move the note to the docs and restate get, as #1872 ruled.