Make H1 sizes consistent between different page types (#777)

### Prerequisites

Put an `x` into the box(es) that apply:

- [x] This pull request fixes a bug.
- [ ] This pull request adds a feature.
- [ ] This pull request introduces breaking change.

### Description

Right now, "article header h1" gets a special larger heading than any
other heading. For consistency's sake, all headings should have the same
size.

This change does not override all H1s otherwise headings generated
halfway down a page with a single '#' in markdown would look weirdly
large. It also does not change all pages to use the article tag, since
the specification states an article must be independently excerpt-able
content, and I would not say that any flavour text above a page listing
is, by itself, an article (e.g. the stuff that you might put as content
for list.html probably doesn't stand alone as an article).

Instead, this chooses to just resize anything which meets the semantic
element of "header h1" (and it adds the semantic element in places where
a header should really be acknowledged as a header, such as on some of
the partials).

### Issues Resolved

https://github.com/luizdepra/hugo-coder/discussions/776

### Checklist

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#### General

- [x] Describe what changes are being made
- [x] Explain why and how the changes were necessary and implemented
respectively
- [x] Reference issue with `#<ISSUE_NO>` if applicable

#### Resources

- [x] If you have changed any SCSS code, run `make release` to
regenerate all CSS files

#### Contributors

- [x] Add yourself to `CONTRIBUTORS.md` if you aren't on it already