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/config/loader.py

@@ -0,0 +1,150 @@
+"""Configuration loader with environment variable substitution."""
+
+from __future__ import annotations
+
+import os
+import re
+from pathlib import Path
+from typing import Any
+
+import yaml
+
+from .models import LiteLLMConfig
+
+# Default configuration path
+DEFAULT_CONFIG_PATH = Path.home() / ".ccw" / "config" / "litellm-config.yaml"
+
+# Global configuration singleton
+_config_instance: LiteLLMConfig | None = None
+
+
+def _substitute_env_vars(value: Any) -> Any:
+    """Recursively substitute environment variables in configuration values.
+
+    Supports ${ENV_VAR} and ${ENV_VAR:-default} syntax.
+
+    Args:
+        value: Configuration value (str, dict, list, or primitive)
+
+    Returns:
+        Value with environment variables substituted
+    """
+    if isinstance(value, str):
+        # Pattern: ${VAR} or ${VAR:-default}
+        pattern = r"\$\{([^:}]+)(?::-(.*?))?\}"
+
+        def replace_var(match: re.Match) -> str:
+            var_name = match.group(1)
+            default_value = match.group(2) if match.group(2) is not None else ""
+            return os.environ.get(var_name, default_value)
+
+        return re.sub(pattern, replace_var, value)
+
+    if isinstance(value, dict):
+        return {k: _substitute_env_vars(v) for k, v in value.items()}
+
+    if isinstance(value, list):
+        return [_substitute_env_vars(item) for item in value]
+
+    return value
+
+
+def _get_default_config() -> dict[str, Any]:
+    """Get default configuration when no config file exists.
+
+    Returns:
+        Default configuration dictionary
+    """
+    return {
+        "version": 1,
+        "default_provider": "openai",
+        "providers": {
+            "openai": {
+                "api_key": "${OPENAI_API_KEY}",
+                "api_base": "https://api.openai.com/v1",
+            },
+        },
+        "llm_models": {
+            "default": {
+                "provider": "openai",
+                "model": "gpt-4",
+            },
+            "fast": {
+                "provider": "openai",
+                "model": "gpt-3.5-turbo",
+            },
+        },
+        "embedding_models": {
+            "default": {
+                "provider": "openai",
+                "model": "text-embedding-3-small",
+                "dimensions": 1536,
+            },
+        },
+    }
+
+
+def load_config(config_path: Path | str | None = None) -> LiteLLMConfig:
+    """Load LiteLLM configuration from YAML file.
+
+    Args:
+        config_path: Path to configuration file (default: ~/.ccw/config/litellm-config.yaml)
+
+    Returns:
+        Parsed and validated configuration
+
+    Raises:
+        FileNotFoundError: If config file not found and no default available
+        ValueError: If configuration is invalid
+    """
+    if config_path is None:
+        config_path = DEFAULT_CONFIG_PATH
+    else:
+        config_path = Path(config_path)
+
+    # Load configuration
+    if config_path.exists():
+        try:
+            with open(config_path, "r", encoding="utf-8") as f:
+                raw_config = yaml.safe_load(f)
+        except Exception as e:
+            raise ValueError(f"Failed to load configuration from {config_path}: {e}") from e
+    else:
+        # Use default configuration
+        raw_config = _get_default_config()
+
+    # Substitute environment variables
+    config_data = _substitute_env_vars(raw_config)
+
+    # Validate and parse with Pydantic
+    try:
+        return LiteLLMConfig.model_validate(config_data)
+    except Exception as e:
+        raise ValueError(f"Invalid configuration: {e}") from e
+
+
+def get_config(config_path: Path | str | None = None, reload: bool = False) -> LiteLLMConfig:
+    """Get global configuration singleton.
+
+    Args:
+        config_path: Path to configuration file (default: ~/.ccw/config/litellm-config.yaml)
+        reload: Force reload configuration from disk
+
+    Returns:
+        Global configuration instance
+    """
+    global _config_instance
+
+    if _config_instance is None or reload:
+        _config_instance = load_config(config_path)
+
+    return _config_instance
+
+
+def reset_config() -> None:
+    """Reset global configuration singleton.
+
+    Useful for testing.
+    """
+    global _config_instance
+    _config_instance = None