feat(providers): add Synthorai as an OpenAI-compatible provider

Synthorai (https://synthorai.io) reaches Anthropic, OpenAI, Google, Z.ai,
Moonshot, DeepSeek and Qwen models through one OpenAI-compatible base URL,
billed at each upstream's own list price.

README.md

@@ -375,6 +375,7 @@ Fabric supports a wide range of AI providers:
 - Novita AI
 - OpenRouter
 - SiliconCloud
+- Synthorai
 - Together
 - Venice AI
 - Z AI

README.zh.md

@@ -358,7 +358,7 @@ fabric --setup
 
 **OpenAI 兼容供应商：**
 
-- Abacus、AIML、Cerebras、DeepSeek、DigitalOcean、GitHub Models、GrokAI、Groq、Langdock、LiteLLM、MiniMax、Mistral、Novita AI、OpenRouter、SiliconCloud、Together、Venice AI、Z AI
+- Abacus、AIML、Cerebras、DeepSeek、DigitalOcean、GitHub Models、GrokAI、Groq、Langdock、LiteLLM、MiniMax、Mistral、Novita AI、OpenRouter、SiliconCloud、Synthorai、Together、Venice AI、Z AI
 
 运行 `fabric --setup` 配置首选供应商，或使用 `fabric --listvendors` 查看所有可用供应商。
 

internal/plugins/ai/openai_compatible/providers_config.go

@@ -294,6 +294,11 @@ var ProviderMap = map[string]ProviderConfig{
 		BaseURL:             "https://api.siliconflow.cn/v1",
 		ImplementsResponses: false,
 	},
+	"Synthorai": {
+		Name:                "Synthorai",
+		BaseURL:             "https://synthorai.io/v1",
+		ImplementsResponses: false,
+	},
 	"Together": {
 		Name:                "Together",
 		BaseURL:             "https://api.together.xyz/v1",