fix(snackbar): always tab to snackbar if active

[ychhabra-eightfold]

SUMMARY:

This PR improves the accessibility of the Snackbar component by simplifying the tab focus behavior. Previously, the component used a firstTabPressedRef to track whether Tab had been pressed once, which prevented users from tabbing back to the snackbar after navigating away.

Changes:

• Removed firstTabPressedRef state tracking
• Simplified keyboard event handler to always redirect Tab press to the first closable snackbar's close button
• Removed the effect that reset the ref when no closable snacks existed

Impact:
Users can now consistently tab to the snackbar's close button whenever they press Tab while a snackbar is visible, making the component more predictable and accessible.

GITHUB ISSUE (Open Source Contributors)

N/A

JIRA TASK (Eightfold Employees Only):

N/A

CHANGE TYPE:

• Bugfix Pull Request
• Feature Pull Request

TEST COVERAGE:

• Tests for this change already exist
• I have added unittests for this change

TEST PLAN:

1. Run Storybook: yarn storybook
2. Navigate to the Snackbar component
3. Trigger a closable snackbar
4. Press Tab key multiple times
5. Verify that each Tab press focuses the first closable snackbar's close button
6. Press Escape to dismiss
7. Verify that Tab behavior works consistently across multiple snackbar displays

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