Move API credentials to .env and set gpt-5.6-luna model

- Load OPENAI_API_KEY and OPENAI_BASE_URL from gitignored .env (repo-root, CWD-independent)
- Fix command explanation to use the configured model instead of hardcoded gpt-4o-mini
- Update default model and fallbacks to gpt-5.6-luna
- Document .env-based configuration in READMEs

edison/core/api_client.py

@@ -11,6 +11,31 @@ from edison.utils import logging_utils
 
 logger = logging.getLogger(__name__)
 
+def get_env_path():
+    """
+    Get the path to the project's `.env` file, independent of the current working directory.
+
+    Returns:
+        str: The absolute path to the `.env` file at the repository root.
+    """
+    project_root = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+    return os.path.join(project_root, ".env")
+
+def get_base_url(config):
+    """
+    Get the API base URL from the environment or config.
+
+    Prefers the `OPENAI_BASE_URL` environment variable, falling back to the
+    `base_url` value in the provided config dictionary.
+
+    Args:
+        config (dict): A dictionary containing configuration values.
+
+    Returns:
+        str or None: The API base URL, or None if not set.
+    """
+    return os.getenv("OPENAI_BASE_URL") or config.get("base_url")
+
 def get_api_key(config):
     """
     Get the OpenAI API key from various sources.
@@ -26,7 +51,7 @@ def get_api_key(config):
     Returns:
         str: The OpenAI API key
     """
-    dotenv.load_dotenv()
+    dotenv.load_dotenv(get_env_path())
 
     # Method 1: Read API key from environment variable
     # The user can set their OpenAI API key by creating a ".env" file in the same
@@ -68,6 +93,9 @@ def create_client(config):
         OpenAI: An initialized OpenAI client.
     """
     api_key = get_api_key(config)
+    base_url = get_base_url(config)
+    if base_url:
+        return OpenAI(api_key=api_key, base_url=base_url)
     return OpenAI(api_key=api_key)
 
 def call_api(client, config, query):
@@ -95,7 +123,7 @@ def call_api(client, config, query):
     try:
         # Use the modern API pattern
         response = client.chat.completions.create(
-            model=config.get("model", "gpt-4o-mini"),
+            model=config.get("model", "gpt-5.6-luna"),
             messages=[
                 {"role": "system", "content": system_prompt},
                 {"role": "user", "content": prompt}
@@ -137,7 +165,7 @@ def call_api_streaming(client, config, query, callback):
     try:
         # Use the streaming API pattern
         response = client.chat.completions.create(
-            model=config.get("model", "gpt-4o-mini"),
+            model=config.get("model", "gpt-5.6-luna"),
             messages=[
                 {"role": "system", "content": system_prompt},
                 {"role": "user", "content": prompt}