Add DocC catalog, docs verification workflow, and editor support docs

[andywkff]

Summary

Add first-class package documentation and tooling support on top of the existing markdown docs and Quick Help comments.

Scope

• Add a SimpleChart.docc catalog with a landing page and focused articles for getting started and interactive chart APIs.
• Polish high-value Quick Help for the interaction/navigation surface so Xcode symbol docs are more teachable.
• Add a GitHub Actions workflow that verifies documentation builds cleanly.
• Add an editor-support note covering Xcode and sourcekit-lsp usage for the SwiftPM package.

Acceptance criteria

• The repo contains a DocC catalog under the SimpleChart target.
• README/docs link users toward the new IDE-native docs and editor support note.
• CI verifies the documentation build path.
• Local task artifacts and issue progress are updated with the final verification results.

[andywkff]

Completed the docs/tooling slice for IDE-native package documentation.

Shipped:

• Added a first-party SimpleChart.docc catalog with landing and focused articles for getting started, wrapper selection, interactive charts, and legacy migration.
• Added docs/editor-support.md covering Xcode Quick Help, local DocC rendering, and sourcekit-lsp expectations.
• Expanded Quick Help on the zoom/navigation surface, including SCChartTimeViewport, SCChartScrollBehavior, SCChartZoomBehavior, SCChartGestureConfiguration, and the scrollable wrappers.
• Added a GitHub Actions Documentation workflow that runs xcodebuild docbuild for the SwiftPM scheme on macOS.
• Updated README/getting-started/changelog references so the DocC catalog and editor support guidance are discoverable.

Verification:

• swift build
• swift test
• xcodebuild docbuild -scheme SimpleChart -destination 'platform=macOS' -derivedDataPath .build/DerivedData CODE_SIGNING_ALLOWED=NO

Result: package build passed, all 73 tests passed, and the DocC build succeeded.