chore: chat/v1/chat.proto

[Junyi-99]

Transformation from LanguageModel to modelSlug.

At this stage, both LanguageModel and modelSlug are allowed to appear simultaneously.

For older versions of the plugin, send the LanguageModel parameter.

For newer versions of the plugin, send the modelSlug parameter.

In the future, we will gradually remove the LanguageModel field.

[Copilot]

Pull request overview

This PR transitions the chat API from using an enum-based LanguageModel to a string-based modelSlug field for model identification. The existing LanguageModel enum is deprecated but retained for backward compatibility, while the new model_slug field provides more flexibility for specifying AI models.

Key changes:

• Added model_slug as a new optional field alongside the deprecated language_model enum in conversation-related messages
• Updated the API to use oneof for model specification, allowing either enum or string-based model selection
• Modified internal handlers to accept and propagate both modelSlug string and optional languageModel pointer
• Regenerated protobuf code with updated protoc-gen-es (v2.10.2) and protoc-gen-go (v1.36.11) versions

Reviewed changes

Copilot reviewed 22 out of 23 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
proto/chat/v1/chat.proto	Added model_slug field to Conversation, CreateConversationMessageRequest, StreamInitialization, and CreateConversationMessageStreamRequest; converted model specification to oneof type
pkg/gen/api/chat/v1/chat.pb.go	Regenerated Go protobuf code with oneof wrappers for model selection
webapp/_webapp/src/pkg/gen/apiclient/chat/v1/chat_pb.ts	Regenerated TypeScript protobuf code with oneof model types
internal/services/toolkit/handler/stream.go	Updated StreamHandler to accept both modelSlug string and optional languageModel pointer
internal/services/toolkit/client/utils.go	Refactored getDefaultParams to use modelSlug strings instead of LanguageModel enum
internal/services/toolkit/client/completion.go	Updated ChatCompletion and ChatCompletionStream signatures to accept modelSlug
internal/api/chat/create_conversation_message.go	Modified prepare and createConversation to handle both model formats with backward compatibility
internal/models/conversation.go	Added ModelSlug field to Conversation struct
internal/services/chat.go	Updated InsertConversationToDB to accept and store modelSlug
go.mod	Added github.com/openai/openai-go/v3 v3.12.0 dependency

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