[Preview] Fix missing view labels in overlay

[heathdutton]

Closes #7712

Describe your changes:

PR #7632 changed the preview header to pass the view instance instead of the view provider to ViewSwitcher and NotebookMenuSwitcher. The view instance (returned by provider.view()) doesn't carry name, cssClass, or key -- those live on the provider. This caused blank labels in the view switcher dropdown when previewing historical data.

This fix passes the view provider separately for display purposes, while keeping the view instance for the action collection watcher which needs it.

Also fixes :v-if (prop binding, always renders) to v-if (directive, conditionally renders) on the ViewSwitcher.

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[Copilot]

Pull request overview

This PR fixes missing view labels in the preview overlay that were introduced by PR #7632. The previous change passed view instances instead of view providers to UI components, but view instances don't carry display metadata like name, cssClass, or key.

Changes:

• Adds a separate currentViewProvider prop to preserve view provider data for display purposes
• Fixes incorrect :v-if prop binding to proper v-if directive in ViewSwitcher
• Maintains the view instance for ActionCollection functionality while passing the provider for display

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/ui/preview/PreviewHeader.vue	Adds currentViewProvider prop and passes it to ViewSwitcher and NotebookMenuSwitcher; fixes :v-if to v-if
src/ui/preview/PreviewContainer.vue	Passes the view provider to PreviewHeader via new current-view-provider prop

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