feat(chat): add DeleteMessage gRPC RPC

[JohnChantz]

Summary

• Adds Chat.DeleteMessage, matching EditMessage, so other modules can delete a message and still emit message-deleted on the chat namespace.
• Moves the client delete path into deleteChatMessage: sender check, allowMessageDelete, auditMode hard-delete vs deleted: true, socket push, and bus publish.

Test plan

• modules/chat unit tests for hard-delete, audit-mode soft-delete, missing message, non-sender, and allowMessageDelete: false
• Publish @conduitplatform/grpc-sdk and @conduitplatform/module-tools 0.16.31 from the v0.16.x backport before Viz main-service depends on deleteMessage

[ChrisPdgn]

@JohnChantz CI check failed on this head (8e0b6f02): security/snyk (kkopanidis) — error, “1 test has failed”.

https://app.snyk.io/org/kkopanidis/pr-checks/1f46beda-fe28-4a24-881c-32f4bdf310f5