Add inline comments and update README for MusicGPT workflow

config.py

@@ -13,6 +13,7 @@ Environment variables (defaults shown):
     - ADMIN_PASSWORD      plain-text password for /admin login
     - PUBLIC_BASE_URL     public URL customers use (e.g. https://booth.example.com)
     - SMTP_PASS           password for the SMTP account
+    - MUSICGPT_API_KEY    API key for MusicGPT generation and polling
   Optional:
     - BOOTH_NAME          name in customer text and emails (default Trollgorithm Theme Songs)
     - HOST_PORT           docker-compose host-side port mapping (default 127.0.0.1:8000)
@@ -27,6 +28,9 @@ Environment variables (defaults shown):
     - SMTP_PORT           outgoing mail server port (default 465)
     - SMTP_USER           SMTP login username (default ai@hallsworth.ca)
     - SMTP_FROM           From address for customer emails (default ai@hallsworth.ca)
+    - HERMES_API_KEY      API key for the /api/prompt callback (optional, can be set in settings)
+    - MUSICGPT_DEFAULT_MODEL  default model selected in the admin dropdown (default v6-pro)
+    - MUSICGPT_MODELS     comma-separated list of models available to the API key (default v6,v6-pro)
 """
 
 import os
@@ -101,7 +105,8 @@ class Config:
     # MusicGPT API key (env only; never stored in repo).
     MUSICGPT_API_KEY = os.environ.get('MUSICGPT_API_KEY', '')
 
-    # Available MusicGPT generation models.
+    # Available MusicGPT generation models. The deployed API key only supports
+    # v6 and v6-pro, so we keep the list explicit rather than making it dynamic.
     MUSICGPT_MODELS = ['v6', 'v6-pro']
     MUSICGPT_DEFAULT_MODEL = os.environ.get('MUSICGPT_DEFAULT_MODEL', 'v6-pro')