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/edison.yaml

@@ -1,7 +1,10 @@
-model: gpt-4o-mini  # Default model for command generation
+model: gpt-5.6-luna  # Default model for command generation
 temperature: 0
 max_tokens: 500
 
+# API base URL (optional): Set via OPENAI_BASE_URL in .env, or uncomment below
+# base_url: https://api.openai.com/v1
+
 # Safety: If set to False, commands returned from the AI will be run *without* prompting the user.
 safety: True
 
@@ -27,5 +30,7 @@ ui:
   # Structured explanations: Generate more structured command explanations
   structured_explanations: True
 
-# Open AI API Key (optional): The key can aso be provided via environment variable (OPENAI_API_KEY), .env, or ~/.openai.apikey file
-openai_api_key:
+# OpenAI API Key (optional): The key can be provided via .env (OPENAI_API_KEY),
+# an environment variable, or the ~/.openai.apikey file. Prefer .env so the key
+# is not checked into version control.
+# openai_api_key: your-api-key-here