[Feature] Add Synthorai model provider

[cuihuan]

Environment Information

MaxKB Version: N/A (feature request, not tied to a specific running instance)

Detailed information

Please describe your needs or suggestions for improvements

Requesting a new model provider for Synthorai (https://synthorai.io), following the same pattern as the recently-added MiniMax (#4876) and Regolo.ai (#3041) providers.

Synthorai is an OpenAI/Anthropic-compatible LLM gateway routing to 113 models across 11 upstream providers (Claude, GPT, Gemini, GLM, Kimi, DeepSeek, Qwen, etc.) at direct upstream pricing, no markup. API docs: https://synthorai.io/docs.

Please describe the solution you suggest

Add apps/setting/models_provider/impl/synthorai_model_provider/ following the same structure as the Regolo.ai provider — LLM credential form with api_key + api_base fields, base URL defaulting to https://synthorai.io/v1, plain OpenAI-compatible request handling (no custom transformation needed).

Additional Information

• Base URL: https://synthorai.io/v1, standard Bearer auth
• Free tier for testing: 10 calls / up to $1, no card required
• Happy to attempt the PR myself, but this touches Django backend patterns (credential forms, model provider registration) I wanted to confirm the right shape for before submitting, given the file count involved in the Regolo.ai precedent.

[cuihuan]

Belated but important disclosure: I'm affiliated with Synthorai — this request adds support for our own product, it isn't me reporting demand from elsewhere. I should have said so in the original post; flagging it now so the ask is judged on its merits with that context on the table.

No expectation of priority attached. Happy to do the implementation work myself, and equally happy to take "not now" for an answer.

[liqiang-fit2cloud]

No plan to support this.