Accessibility Select - Can't navigate to select with keyboard if in initially closed panel

Describe the bug

There is an issue with keyboard accessibility when Select is used inside initially collapsed Panel.
When Panels input collapsed initially is set to false keyboard accessibility works as exptected.

Pull Request Link

No response

Reason for not contributing a PR

• Lack of time
• Unsure how to implement the fix/feature
• Difficulty understanding the codebase
• Other

Other Reason

No response

Reproducer

https://stackblitz.com/edit/uvcatr26?file=src%2Fapp%2Fpanel-toggleable-demo.html,src%2Fapp%2Fpanel-toggleable-demo.ts

Environment

Win11

Angular version

19.0.1

PrimeNG version

v19

Node version

No response

Browser(s)

No response

Steps to reproduce the behavior

1. Go to https://stackblitz.com/edit/uvcatr26?file=src%2Fapp%2Fpanel-toggleable-demo.html,src%2Fapp%2Fpanel-toggleable-demo.ts,package.json
2. Expand Panel using + icon.
3. Try to navigate to Select using 'Tab' key on keyboard.
4. Unable to navigate to Select.

If you change filterCollapsed value to false:

you will be able to navigate to select using 'Tab' key on keyboard.

For some reason tabindex input of select is ignored in first scenario.

Expected behavior

User should be able to navigate to Select using keyboard even if panel is initially closed.

Start with the StackBlitz reproducer files src/app/panel-toggleable-demo.html and src/app/panel-toggleable-demo.ts, and compare keyboard navigation when the Panel is initially collapsed versus expanded. Trace the Select and Panel accessibility behavior, then verify that expanding the initially closed Panel allows Tab to reach the Select.