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/ui/console.py

@@ -132,7 +132,7 @@ def handle_command_execution(client, config, command, explain=False):
             use_rich = ui_config.get("rich_formatting", True)
             
             # Generate explanation
-            explanation = get_command_explanation(client, command, structured=structured)
+            explanation = get_command_explanation(client, command, structured=structured, model=config.get("model"))
             
             if use_rich:
                 print()  # Add a blank line before the explanation

edison/ui/interactive.py

@@ -25,7 +25,7 @@ def handle_streaming_output_interactive(token):
     # Print the token without a newline and flush immediately
     print(token, end='', flush=True)
 
-def get_command_explanation(client, command, structured=False):
+def get_command_explanation(client, command, structured=False, model=None):
     """
     Get an explanation for a command.
     
@@ -33,6 +33,7 @@ def get_command_explanation(client, command, structured=False):
         client: The OpenAI client.
         command (str): The command to explain.
         structured (bool): Whether to use structured explanation format.
+        model (str): The model to use for explanation.
         
     Returns:
         str: The explanation of the command.
@@ -61,7 +62,7 @@ def get_command_explanation(client, command, structured=False):
             """
         
         response = client.chat.completions.create(
-            model="gpt-4o-mini",
+            model=model or "gpt-5.6-luna",
             messages=[
                 {"role": "system", "content": system_prompt},
                 {"role": "user", "content": command}
@@ -284,7 +285,7 @@ def interactive_mode(client, config):
                     use_rich = ui_config.get("rich_formatting", True)
                     
                     # Generate explanation
-                    explanation = get_command_explanation(client, command, structured=structured)
+                    explanation = get_command_explanation(client, command, structured=structured, model=config.get("model"))
                     
                     if use_rich:
                         print()  # Add a blank line before the explanation