Add a polished onboarding modal wizard with persisted state and deep linking

[grantfox-oss]

Problem

The app needs a stronger first-time onboarding experience for new users.

Goals

• Build a multi-step onboarding wizard using components/ui/dialog.tsx or Radix Dialog primitives.
• Persist onboarding progress in local storage and allow resuming the flow later.
• Add optional deep-link states that open a specific step from a URL query.

Acceptance criteria

• The onboarding wizard opens from a CTA and supports next/back navigation.
• Progress is saved locally and restored after reload.
• URL state like ?onboarding=step-2 navigates to the appropriate step.
• The experience is accessible, including focus management and announcements.

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[GBOYEE]

Hi — a first-time onboarding wizard with resumable progress is a big activation win. I can build the multi-step dialog (Radix primitives), persist step state to local storage, and add the deep-link query params so a specific step can be opened from a URL. Happy to claim this one.

[canicefavour]

I can implement this multi-step onboarding flow, having built similar accessible React onboarding experiences before, by using the existing Dialog components with persistent local progress, deep-linkable step navigation, robust focus management, and seamless resume support across page reloads.

[grantfox-oss]

🦊 GrantFox — @canicefavour has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #533)
2. Your PR will be reviewed by the MERIDIAN-CITY maintainers

Good luck! Track your progress on GrantFox.