docs(api): improve clarity of .env.example comments

Updates the comments in the `.env.example` file to be more explicit
and unambiguous. The new comments clearly state when each variable is
required (e.g., "REQUIRED" vs. "REQUIRED FOR PRODUCTION") and provide
better context for their purpose. This resolves confusion around the
previous "Optional for Production" wording.

Author: fulleni

.env.example

@@ -2,9 +2,11 @@
 # Copy this file to .env and fill in your actual configuration values.
 # The .env file is ignored by Git and should NOT be committed.
 
+# REQUIRED: The full connection string for your MongoDB instance.
+# The application cannot start without a database connection.
 # DATABASE_URL="mongodb://user:password@localhost:27017/ht_api_db"
 
-# (Optional for Production) The specific origin URL of your web client (e.g., the HT Dashboard).
-# This is required for production deployments to allow cross-origin requests.
+# REQUIRED FOR PRODUCTION: The specific origin URL of your web client.
+# This allows the client (e.g., the HT Dashboard) to make requests to the API.
 # For local development, this can be left unset as 'localhost' is allowed by default.
 # CORS_ALLOWED_ORIGIN="https://your-dashboard.com"