feat(tui): add SiliconFlow provider

[qychen2001]

Add SiliconFlow (https://siliconflow.com) as a new API provider with OpenAI-compatible /v1/chat/completions endpoint.

• Base URL: https://api.siliconflow.com/v1
• Default model: deepseek-ai/DeepSeek-V4-Pro
• Supports thinking (reasoning) and cache telemetry
• Pass-through model names (no remapping)
• Env vars: SILICONFLOW_API_KEY, SILICONFLOW_BASE_URL, SILICONFLOW_MODEL
• Provider aliases: siliconflow, sf

Summary

Testing

• cargo test --all-features
• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features

Checklist

• Updated docs or comments as needed
• Added or updated tests where relevant
• Verified TUI behavior manually if UI changes

[gemini-code-assist]

Code Review

This pull request adds SiliconFlow as a new AI provider, updating configuration files, environment variable handling, and TUI components to support its API. Key updates include the addition of SiliconFlow to provider enums, implementation of its default settings, and integration into the reasoning and telemetry logic. The reviewer recommended updating a stale comment about cache telemetry and including the SiliconFlow-specific default model in the model picker's completion list to improve usability.

[gemini-code-assist]

The comment on line 304 is now outdated as it doesn't mention SiliconFlow. It should be updated to: // Cache telemetry: returned only by DeepSeek-native, NVIDIA NIM, and SiliconFlow endpoints.

[gemini-code-assist]

For the SiliconFlow provider, it would be beneficial to include its default model (deepseek-ai/DeepSeek-V4-Pro) in the completion list, as it differs from the standard DeepSeek model names used by other providers. This improves the user experience when using the model picker.

        ApiProvider::Openai | ApiProvider::Atlascloud | ApiProvider::Ollama => {
            OFFICIAL_DEEPSEEK_MODELS.to_vec()
        }
        ApiProvider::SiliconFlow => {
            let mut models = OFFICIAL_DEEPSEEK_MODELS.to_vec();
            models.push(DEFAULT_SILICONFLOW_MODEL);
            models
        }