feat: Add Avian as an LLM provider (#13256)

### What problem does this PR solve?

This PR adds [Avian](https://avian.io) as a new LLM provider to RAGFlow.
Avian provides an OpenAI-compatible API with competitive pricing,
offering access to models like DeepSeek V3.2, Kimi K2.5, GLM-5, and
MiniMax M2.5.

**Provider details:**
- API Base URL: `https://api.avian.io/v1`
- Auth: Bearer token via API key
- OpenAI-compatible (chat completions, streaming, function calling)
- Models:
  - `deepseek/deepseek-v3.2` — 164K context, $0.26/$0.38 per 1M tokens
  - `moonshotai/kimi-k2.5` — 131K context, $0.45/$2.20 per 1M tokens
  - `z-ai/glm-5` — 131K context, $0.30/$2.55 per 1M tokens
  - `minimax/minimax-m2.5` — 1M context, $0.30/$1.10 per 1M tokens

**Changes:**
- `rag/llm/chat_model.py` — Add `AvianChat` class extending `Base`
- `rag/llm/__init__.py` — Register in `SupportedLiteLLMProvider`,
`FACTORY_DEFAULT_BASE_URL`, `LITELLM_PROVIDER_PREFIX`
- `conf/llm_factories.json` — Add Avian factory with model definitions
- `web/src/constants/llm.ts` — Add to `LLMFactory` enum, `IconMap`,
`APIMapUrl`
- `web/src/components/svg-icon.tsx` — Register SVG icon
- `web/src/assets/svg/llm/avian.svg` — Provider icon
- `docs/references/supported_models.mdx` — Add to supported models table

This follows the same pattern as other OpenAI-compatible providers
(e.g., n1n #12680, TokenPony).

cc @KevinHuSh @JinHai-CN

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

rag/llm/__init__.py

@@ -58,6 +58,7 @@ class SupportedLiteLLMProvider(StrEnum):
     Azure_OpenAI = "Azure-OpenAI"
     n1n = "n1n"
     HunYuan = "Tencent Hunyuan"
+    Avian = "Avian"
 
 
 FACTORY_DEFAULT_BASE_URL = {
@@ -85,6 +86,7 @@ FACTORY_DEFAULT_BASE_URL = {
     SupportedLiteLLMProvider.OpenAI: "https://api.openai.com/v1",
     SupportedLiteLLMProvider.n1n: "https://api.n1n.ai/v1",
     SupportedLiteLLMProvider.HunYuan: "https://api.hunyuan.cloud.tencent.com/v1",
+    SupportedLiteLLMProvider.Avian: "https://api.avian.io/v1",
 }
 
 
@@ -124,6 +126,7 @@ LITELLM_PROVIDER_PREFIX = {
     SupportedLiteLLMProvider.Azure_OpenAI: "azure/",
     SupportedLiteLLMProvider.n1n: "openai/",
     SupportedLiteLLMProvider.HunYuan: "openai/",
+    SupportedLiteLLMProvider.Avian: "openai/",
 }
 
 ChatModel = globals().get("ChatModel", {})

rag/llm/chat_model.py

@@ -1096,6 +1096,15 @@ class N1nChat(Base):
         super().__init__(key, model_name, base_url, **kwargs)
 
 
+class AvianChat(Base):
+    _FACTORY_NAME = "Avian"
+
+    def __init__(self, key, model_name, base_url="https://api.avian.io/v1", **kwargs):
+        if not base_url:
+            base_url = "https://api.avian.io/v1"
+        super().__init__(key, model_name, base_url, **kwargs)
+
+
 class LiteLLMBase(ABC):
     _FACTORY_NAME = [
         "Tongyi-Qianwen",