Pre defined headings

Currently we only have the `Heading` component that only outputs an h2 html element. We should add individual components for h1-h6 with pre-defined (opinionated) sizes. These components should use the `Heading` component internally. Should also add a setting in `Heading` to output h1-h6

Start by locating the existing Heading component and reviewing how its HTML element and styles are defined. Add individual h1–h6 components that reuse Heading, provide opinionated sizes, and support selecting h1–h6 through Heading itself; verify the rendered elements and styling across all six levels.

Written by the indexing model from the issue text.