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/README.md

@@ -80,7 +80,7 @@ The rich terminal UI provides:
 Edison can be configured via the `edison.yaml` file. Here's an example configuration:
 
 ```yaml
-model: gpt-3.5-turbo
+model: gpt-5.6-luna
 temperature: 0
 max_tokens: 500
 safety: true
@@ -88,13 +88,22 @@ safety: true
 
 ## API Key
 
-Edison requires an OpenAI API key to function. You can provide it in one of the following ways:
+Edison requires an API key to function. The recommended way is a `.env` file in the repository root (gitignored, so not checked in):
+
+```
+OPENAI_API_KEY="your-api-key"
+OPENAI_BASE_URL="https://api.openai.com/v1"
+```
+
+You can also provide it in one of the following ways:
 
 1. Environment variable: `OPENAI_API_KEY="your-api-key"`
-2. `.env` file in the same directory as the script
+2. `.env` file in the repository root
 3. `.openai.apikey` file in your home directory
 4. In the `edison.yaml` configuration file: `openai_api_key: "your-api-key"`
 
+When using a custom backend or proxy, set `OPENAI_BASE_URL` (or `base_url` in `edison.yaml`) to its endpoint.
+
 ## License
 
 MIT