Sample content: page descriptions restate titles; stale versions in the contribution guidelines

[chalin]

A few sample pages carry a description that restates the title or the lead rather than complementing it:

• content/en/about/index.md: the description repeats the page's opening sentence (and renders in the cover block too)
• content/en/site.md: "Information about the website" vs the title "Website information"
• content/en/docs/contribution-guidelines.md: "How to contribute to the docs" restates the title

Related stale sample text in contribution-guidelines.md: the Hugo "version 0.146.0" sentence (the site's minimum is 0.160.1) and the git clone --branch v0.12.0 example.

Found during the review of #519; left out of that PR as unrelated sample-content hygiene.

[chalin]

More sample-content hygiene from the #519 review rounds, same bucket:

• hugo.yaml: the legacy top-level pygments* keys duplicate markup.highlight (tango is set twice) and pygmentsUseClasses: false contradicts noClasses: false; the "Use the new Chroma Go highlighter" comment above them is stale. Dropping the pygments* block (superseded since Hugo 0.60) leaves one home.
• Content links hard-code the repository URLs that params.github_repo / github_project_repo already own (14 links across 9 pages); content/en/site.md shows the param-in-link-def pattern that would make "point this at your own repo" a one-line edit.
• content/fa/docs/_index.md: linkTitle equals title; content/en/docs/_index.md has no description (renders bare in the section index and in llms.txt).
• Two hyphen-as-dash sentences: content/en/docs/_index.md ("lives - all the") and contribution-guidelines.md ("get one - click").