docs(agents): align sender workflow endpoint guidance with upsert API

- replace outdated draft/update/send endpoint list with current POST /api/Envelope workflow contract

AGENTS.md

@@ -152,15 +152,13 @@ float inches = (pixelX / canvasWidth) * pageWidthInches;
 - **Use case:** External API consumers
 - **Not suitable for:** Step-by-step UI workflow (no draft support, no partial updates)
 
-### Missing Granular Endpoints (Need to Create)
+### Sender Workflow Endpoint
 ```
-POST /api/Envelope/draft          # Create draft envelope
-PUT /api/Envelope/{id}            # Update metadata
+POST /api/Envelope                # Create/update/save/send envelope workflow payload
 DELETE /api/Envelope/{id}         # Delete with reason
 POST /api/Envelope/{id}/document  # Upload PDF
 POST /api/Envelope/{id}/receivers # Add receiver
 POST /api/Envelope/{id}/signature-fields  # Place signature field
-POST /api/Envelope/{id}/send      # Send to receivers
 ```
 
 See `FORM_APPLICATION_CONTEXT.md` for detailed workflow requirements.