Draft: fix: add UI feedback for Issue to MR flow

Relates to issue #578654 (closed)

Changes

1. Increased Toast Visibility Duration

• File: ee/app/assets/javascripts/ai/components/duo_workflow_action.vue
• Change: Increased TOAST_HIDE_DELAY from 4000ms to 8000ms (4 seconds → 8 seconds)
• Impact: Users now have twice as long to see and interact with the success notification

2. Optimized Toast Timing

• File: ee/app/assets/javascripts/ai/components/duo_workflow_action.vue
• Change: Reordered the startWorkflow method to call showSuccessToast() immediately after successful API response, before emitting the 'agent-flow-started' event
• Impact: Toast appears as quickly as possible after the workflow starts, ensuring users receive immediate feedback

3. Enhanced Test Coverage

• File: ee/spec/frontend/ai/components/duo_workflow_action_spec.js
• Changes:
  • Updated all existing test expectations to reflect the new 8-second auto-hide delay
  • Added new test suite "toast notification timing" with two test cases verifying:
    • Toast is called before emitting the agent-flow-started event
    • Toast displays immediately with correct parameters (message, action link, and delay)

Expected User Experience

After these changes, when users click "Generate MR with Duo":

1. Button shows loading state for 2-3 seconds (existing behavior)
2. Immediately after successful API response, a toast notification appears with:
   • Message: "Issue to merge request #[id] created"
   • "View" button linking directly to the agent session
   • 8-second display duration (doubled from previous 4 seconds)
3. Users have clear, visible feedback about what happened and where to navigate next