Add SiliconFlow provider

[123xiaode456-boop]

Summary

• Add SiliconFlow as an OpenAI-compatible AI provider.
• Add a SiliconFlow model to the model selector and model API config.
• Route SiliconFlow models in both edit-intent analysis and code generation flows.
• Document SiliconFlow environment variables in the root app and create-open-lovable templates.
• Add a lightweight provider configuration test that verifies SiliconFlow wiring.

Test

node tests/provider-manager-config.test.mjs
node -e "const fs=require('fs'); JSON.parse(fs.readFileSync('package.json','utf8')); console.log('package.json ok')"

Note: this environment does not have npm available, so I could not run the full Next.js lint/build scripts locally.

Related

SiliconFlow task: siliconflow/siliconflow-open-source-tasks#4