chore(contract): sync flipcash2 protos to 3bb442d

[bmc08gt]

Syncs flipcash2 protos from ec66e6b1 to 3bb442d3 (flipcash2-protobuf-api #134) and adds the 0.17.0 changelog entry. Only chat.v1 moved.

Added:

• Metadata.description (= 16): group descriptions, up to 160 characters, moderated like the title.
• description on PublicGroupChatParameters (= 4) and PrivateGroupChatParameters (= 3).
• EditChatRequest.description (= 4), a Description { value } wrapper: unset leaves the description alone, a set wrapper with an empty value clears it.
• MetadataUpdate.DescriptionChanged (= 6).
• DESCRIPTION_MODERATED on StartChatResponse.Result (= 6) and EditChatResponse.Result (= 5), with flagged_category set as for TITLE_MODERATED.

Nothing existing changed: no renames and no renumbering. Both new result cases come after the existing ones. A client with an exhaustive MetadataUpdate switch needs a DescriptionChanged case.

f43272d also regenerates ContractInfo.swift for the new changelog heading (0.17.0-dev).

Both apps build against this branch through the local overrides. Their pin bumps are draft PRs stacked on the 0.16.0 app PRs, waiting on the 0.17.0 release:

• Android: feat(chat): adopt flipcash2 0.17.0 (group descriptions) code-android-app#1684
• iOS: feat(chat): adopt flipcash2 0.17.0 (group descriptions) code-ios-app#975

After merge, run publish.yml at 0.17.0.