fix(explorer): increase consistency, explicitly use font-family (#496)

* fix(explorer): display name for folders without `index` file

* docs(explorer): add section for folder display names

* docs(explorer): fix broken wikilink

* fix(consistency): explicitly set font + label/link fix

Use consistent styling between folders with `folderClickBehavior: "link"` and `"collapse`

* Update quartz/components/styles/explorer.scss

Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>

* Update quartz/components/styles/explorer.scss

Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>

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Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>