Add Label support

[Kyle-Ye]

Summary

Add public Label support for pairing a title with an icon in a style-aware view.

Scope

• Add the generic Label API with title and icon builders.
• Add common Text and Image convenience initializers, including system-image and named-image forms.
• Integrate LabelStyle, style configuration, .labelStyle(_:), and the automatic, title-and-icon, title-only, and icon-only styles.
• Preserve the title and icon content when labels are composed inside controls and containers.
• Add examples and focused coverage for custom and convenience-initialized labels.

Acceptance criteria

• A custom Label { ... } icon: { ... } compiles and renders both components.
• Label("Title", systemImage: "star") renders through the supported image backend.
• Standard label styles select the expected title and icon content.
• Label content remains available to enclosing controls and accessibility processing.

API reference

• Label