feat: Add unified LiteLLM API management with dashboard UI and CLI integration

- Create ccw-litellm Python package with AbstractEmbedder and AbstractLLMClient interfaces
- Add BaseEmbedder abstraction and factory pattern to codex-lens for pluggable backends
- Implement API Settings dashboard page for provider credentials and custom endpoints
- Add REST API routes for CRUD operations on providers and endpoints
- Extend CLI with --model parameter for custom endpoint routing
- Integrate existing context-cache for @pattern file resolution
- Add provider model registry with predefined models per provider type
- Include i18n translations (en/zh) for all new UI elements

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ccw-litellm/src/ccw_litellm/interfaces/llm.py

@@ -0,0 +1,45 @@
+from __future__ import annotations
+
+import asyncio
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import Any, Literal, Sequence
+
+
+@dataclass(frozen=True, slots=True)
+class ChatMessage:
+    role: Literal["system", "user", "assistant", "tool"]
+    content: str
+
+
+@dataclass(frozen=True, slots=True)
+class LLMResponse:
+    content: str
+    raw: Any | None = None
+
+
+class AbstractLLMClient(ABC):
+    """LiteLLM-like client interface.
+
+    Implementers only need to provide synchronous methods; async wrappers are
+    provided via `asyncio.to_thread`.
+    """
+
+    @abstractmethod
+    def chat(self, messages: Sequence[ChatMessage], **kwargs: Any) -> LLMResponse:
+        """Chat completion for a sequence of messages."""
+
+    @abstractmethod
+    def complete(self, prompt: str, **kwargs: Any) -> LLMResponse:
+        """Text completion for a prompt."""
+
+    async def achat(self, messages: Sequence[ChatMessage], **kwargs: Any) -> LLMResponse:
+        """Async wrapper around `chat` using a worker thread by default."""
+
+        return await asyncio.to_thread(self.chat, messages, **kwargs)
+
+    async def acomplete(self, prompt: str, **kwargs: Any) -> LLMResponse:
+        """Async wrapper around `complete` using a worker thread by default."""
+
+        return await asyncio.to_thread(self.complete, prompt, **kwargs)
+