<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Adds an onboarding banner in Setup that links to a 3-minute YouTube
intro and dismisses after click. Also avoids showing release notes on a
user’s first launch.

- **New Features**
- Added OnboardingBanner component with YouTube thumbnail and play icon.
  - Opens the video via IpcClient and hides the banner after click.
  - Integrated into SetupBanner with local visibility state.

- **Bug Fixes**
  - Don’t show release notes on first run to prevent spam.

<!-- End of auto-generated description by cubic. -->

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds a dismissible onboarding banner linking to a YouTube intro and
changes release notes to appear only on app updates, not first run.
> 
> - **UI/Onboarding**:
> - **`src/components/home/OnboardingBanner.tsx`**: New banner component
with YouTube thumbnail/play icon; opens intro video via
`IpcClient.openExternalUrl`; hides itself on click.
> - **`src/components/SetupBanner.tsx`**: Integrates `OnboardingBanner`
with `isOnboardingVisible` state; tweaks header typography
(`font-medium`).
> - **Release Notes Behavior**:
> - **`src/pages/home.tsx`**: Only shows release notes when upgrading
(checks existing `settings.lastShownReleaseNotesVersion` before opening
modal); preserves themed URL handling.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
832e70f87b3b6a7e8b8b921fe8c6ceb15198cce0. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->