A11y: Fix overview group names, expandable nav item type, duplicate popup announcement, and Semantic ComboBox result count

[haoliuu]

Accessibility fixes for AI Dev Gallery. Each commit is a standalone fix and can be reviewed independently.

Fixes

• Announce category group names for overview page cards — the grouped ItemsView on the Scenario/API overview pages now exposes an AutomationProperties.Name, and group titles use HeadingLevel, so Narrator announces each section.
• Announce control type for expandable navigation items — expandable category NavigationViewItems (Scenarios / APIs) append their real control type to the accessible name so Narrator conveys they are expandable groups.
• Avoid double popup announcement for performance details button — the sample performance-details button no longer hosts a Flyout; its content is exposed via tooltip + AutomationProperties.FullDescription, so Narrator no longer announces "popup window" twice.
• Announce Semantic ComboBox result count for screen readers — the Semantic ComboBox announces the result count (e.g. "5 results") once per query via NarratorHelper.Announce, matching the app's main search box.

[Copilot]

Pull request overview

This PR improves screen-reader accessibility across AI Dev Gallery by enhancing UI Automation metadata and Narrator announcements so grouped content, expandable navigation items, and search-like controls convey clearer context to users.

Changes:

• Adds heading levels and automation names for grouped overview sections (Scenarios/APIs) so Narrator announces section names appropriately.
• Enhances accessible naming for expandable NavigationViewItem category groups by appending their localized control type.
• Removes the performance-details flyout in favor of tooltip + AutomationProperties.FullDescription to avoid duplicate “popup” announcements, and adds a Semantic ComboBox result-count announcement.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
AIDevGallery/Samples/SharedCode/Controls/SemanticComboBox.cs	Announces semantic suggestion result counts and guards against stale async results.
AIDevGallery/Pages/Scenarios/ScenarioSelectionPage.xaml.cs	Applies control-type suffixing to scenario category navigation items for clearer SR output.
AIDevGallery/Pages/Scenarios/ScenarioOverviewPage.xaml	Adds heading level + automation naming to grouped scenario overview sections.
AIDevGallery/Pages/APIs/APISelectionPage.xaml.cs	Applies control-type suffixing to API category navigation items (and adds helper import).
AIDevGallery/Pages/APIs/APIOverview.xaml	Adds heading level and automation name to improve SR navigation/announcement.
AIDevGallery/Helpers/NavigationViewItemHelper.cs	Introduces AppendControlTypeToName helper for localized control-type accessible naming.
AIDevGallery/Controls/SampleContainer.xaml.cs	Switches performance-details content exposure to tooltip + FullDescription (no flyout).
AIDevGallery/Controls/SampleContainer.xaml	Updates the performance-details button’s automation properties and removes the flyout content.