Fix site-wide heading hierarchy and search widget H1

[LukasWallrich]

Why this needs addressing

The live homepage and glossary pages emit <h1>Search</h1> before the page-specific headings. The author template likewise renders the profile name as an <h2>, while the search widget remains the first H1. For example, the homepage currently starts with Search, followed by several section H1s; /authors/kimberly-quinn/ has Search as its only H1 and the person’s name as an H2.

Relevant implementation: layouts/partials/search.html emits the search heading, and layouts/authors/list.html renders the profile name.

Requested change

• Change the search widget heading to an appropriate subordinate heading or an accessible labelled container without changing its visual appearance.
• Give the homepage one meaningful page-level H1 and demote its section headings to H2.
• Promote the author name to H1 on author profile pages.
• Check glossary, resource, taxonomy, and post templates for the same pattern.

Acceptance criteria

• The first meaningful heading on each representative page describes that page.
• Author profiles have the person’s name as H1.
• Search remains keyboard- and screen-reader-accessible.
• Add a template-level regression check or fixture so the search widget cannot become the page H1 again.