chore: update .env.example with sendgrid config

- Added SENDGRID_API_KEY
- Added DEFAULT_SENDER_EMAIL
- Added OTP_TEMPLATE_ID
- Added SENDGRID_API_URL (optional)

Author: fulleni

.env.example

@@ -16,11 +16,16 @@
 # For local development, this can be left unset as 'localhost' is allowed by default.
 # CORS_ALLOWED_ORIGIN="https://your-dashboard.com"
 
-# REQUIRED FOR PRODUCTION: The issuer URL for JWTs.
-# Defaults to 'http://localhost:8080' for local development if not set.
-# For production, this MUST be the public URL of your API.
-# JWT_ISSUER="https://api.your-domain.com"
+# REQUIRED: Your SendGrid API key for sending emails.
+# SENDGRID_API_KEY="your-sendgrid-api-key"
 
-# OPTIONAL: The expiry duration for JWTs in hours.
-# Defaults to 1 hour if not set.
-# JWT_EXPIRY_HOURS="24"
+# REQUIRED: The default email address to send emails from.
+# DEFAULT_SENDER_EMAIL="noreply@example.com"
+
+# REQUIRED: The SendGrid template ID for the OTP email.
+# OTP_TEMPLATE_ID="d-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+
+# OPTIONAL: The base URL for the SendGrid API.
+# Defaults to "https://api.sendgrid.com" if not set.
+# Use "https://api.eu.sendgrid.com" for EU-based accounts.
+# SENDGRID_API_URL="https://api.sendgrid.com"