llms.txt: HTML tags in website.title are not stripped

Bug description

When website.title contains HTML tags (e.g. <small>), those tags appear verbatim in the generated llms.txt file. For example, a title like:

website:
  title: "My Site <small>Version 1.0</small>"

produces an llms.txt opening line of:

# My Site <small>Version 1.0</small>

The HTML markup should be stripped so llms.txt contains plain text.

Steps to reproduce

# _quarto.yml
project:
  type: website

website:
  llms-txt: true
  title: "My Site <small>Version 1.0</small>"

format:
  html:
    theme: cosmo

Render and inspect _site/llms.txt — the opening heading contains the raw HTML tag.

Relevant code

The site title is written directly without any HTML stripping:

https://github.com/quarto-dev/quarto-cli/blob/1072f7a9ac737c0170c82205bda7fef4dea862bf/src/project/types/website/website-llms.ts#L387

Notes

Reported by the Connect team, where a documentation site uses <small> in the title alongside an env shortcode. The shortcode resolution part is already handled by #14237. This is the remaining piece: HTML markup in website.title is not stripped before being written to llms.txt.