feat: add SiliconFlow provider support

Add SiliconFlow (硅基流动) as an OpenAI-compatible gateway provider.
SiliconFlow hosts multiple models (Qwen, DeepSeek, etc.) via an
OpenAI-compatible API at https://api.siliconflow.cn/v1.

Changes:
- Add ProviderSpec for siliconflow in providers/registry.py
- Add siliconflow field to ProvidersConfig in config/schema.py

Co-authored-by: Cursor <cursoragent@cursor.com>

nanobot/config/schema.py

@@ -192,6 +192,7 @@ class ProvidersConfig(BaseModel):
     moonshot: ProviderConfig = Field(default_factory=ProviderConfig)
     minimax: ProviderConfig = Field(default_factory=ProviderConfig)
     aihubmix: ProviderConfig = Field(default_factory=ProviderConfig)  # AiHubMix API gateway
+    siliconflow: ProviderConfig = Field(default_factory=ProviderConfig)  # 硅基流动 API gateway
 
 
 class GatewayConfig(BaseModel):

nanobot/providers/registry.py

@@ -117,6 +117,27 @@ PROVIDERS: tuple[ProviderSpec, ...] = (
         model_overrides=(),
     ),
 
+    # SiliconFlow (硅基流动): OpenAI-compatible gateway hosting multiple models.
+    # strip_model_prefix=False: SiliconFlow model names include org prefix
+    # (e.g. "Qwen/Qwen2.5-14B-Instruct", "deepseek-ai/DeepSeek-V3")
+    # which is part of the model ID and must NOT be stripped.
+    ProviderSpec(
+        name="siliconflow",
+        keywords=("siliconflow",),
+        env_key="OPENAI_API_KEY",            # OpenAI-compatible
+        display_name="SiliconFlow",
+        litellm_prefix="openai",             # → openai/{model}
+        skip_prefixes=(),
+        env_extras=(),
+        is_gateway=True,
+        is_local=False,
+        detect_by_key_prefix="",
+        detect_by_base_keyword="siliconflow",
+        default_api_base="https://api.siliconflow.cn/v1",
+        strip_model_prefix=False,
+        model_overrides=(),
+    ),
+
     # === Standard providers (matched by model-name keywords) ===============
 
     # Anthropic: LiteLLM recognizes "claude-*" natively, no prefix needed.