feat: OpenRouter

[Junyi-99]

This pull request introduces a significant refactor to how language models are referenced and handled across the codebase, moving from a legacy enum-based approach to a more flexible string-based "model slug" system. It also upgrades the OpenAI client library to v3 and updates configuration to use a new inference service. Additionally, several new models are now supported, and the handling of conversation history has been modernized for better compatibility and extensibility.

Key changes include:

Model Handling and API Changes:

• Replaced the use of the deprecated LanguageModel enum throughout the API with a new modelSlug string field, updating all relevant function signatures and data structures to use the new approach. This includes fallback logic for backward compatibility. (internal/api/chat/create_conversation_message_stream.go, internal/api/chat/create_conversation_message_stream_helper.go, internal/models/conversation.go, internal/api/mapper/conversation.go) [1] F51da0ccL99, F51da0ccL165, F51da0ccL208, F51da0ccL236, [2] [3]

• Upgraded the OpenAI client from v2 to v3 and refactored all usages and data types accordingly, including the way chat history is stored and sent. (go.mod, internal/api/chat/create_conversation_message_stream_helper.go, internal/models/conversation.go, internal/api/chat/list_supported_models.go) [1] [2] [3] F51da0ccL53, F51da0ccL70, F51da0ccL114, F51da0ccL154, [4] [5] [6] [7]

Supported Models Expansion:

• Added support for new models including GPT-5 nano and Qwen variants, and updated the model slug formatting to use provider-prefixed slugs (e.g., openai/gpt-4o). (internal/api/chat/list_supported_models.go)

Configuration Refactor:

• Changed configuration from OpenAI-specific fields (OpenAIBaseURL, OpenAIAPIKey) to more generic inference service fields (PDInferenceBaseURL, PDInferenceAPIKey) throughout the codebase and tests. (internal/libs/cfg/cfg.go, internal/libs/cfg/cfg_test.go) [1] F5f06866L19, F5f06866L29, [2]

Codebase Cleanup:

• Removed the deprecated CreateConversationMessage method and its supporting code, consolidating all conversation message creation through the streaming API. (internal/api/chat/create_conversation_message_stream_helper.go)

These changes modernize the model selection process, improve extensibility for future models and providers, and align the codebase with the latest OpenAI client and internal infrastructure.

[Junyi-99]

compatible

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