Add AI Chat icon onboarding

[Bunn]

Task/Issue URL: https://app.asana.com/0/1204167627774280/1208607376873996/f
Tech Design URL:
CC:

Description:
Add AI Chat toolbar icon onboarding flow

Steps to Test This PR:

1. To start fresh, navigate to the Debug menu and select "AI Chat Reset."
2. Open the website: https://duck.ai/.
3. If this is your first time using Duck Chat, complete the onboarding process, then open it again in a new tab.
4. Check for a popover prompting you to add the toolbar icon.
5. Click on "Add Shortcut."
6. Confirm that you see a confirmation message and that the icon remains in the window toolbar.
7. Verify that in Settings -> AI Chat, the option to display the icon is selected.
8. Click the icon and ensure that you are redirected to the AI Chat webpage.

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1. Repeat the steps from the first block of tests, but this time open multiple windows. Ensure that the popover is only displayed in the active window.

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1. Follow the same steps as in the first block of tests, but instead of accepting the popover modal, click "No Thanks."
2. Confirm that the icon is not added to the toolbar.
3. Check that in Settings -> AI Chat, the option for the toolbar icon is not selected.

[github-actions]

	Warnings
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

	Messages
📖	You seem to be updating localized strings. Make sure that you request translations and include translated strings before you ship your change. See Localization Guidelines for more information.

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