I (practically) make a distinction between two types of tags:
Tags you add in pages – describe things within the page
Tags you add to pages – describe the page; I call these meta-tags
In my design system, I never mix the two.
I’d find it useful to be able to add meta-tags to pages from the tag pane. Meta-tags could appear in the meta section of the page:
meta-tags: #tag1, #tag2, #tag3
When you open the tag pane for the current page, you’re shown a list of all tags. The meta-tags could be displayed in a different color. The meta-tags that apply to the current page could appear highlighted in the tag pane. You’d have the option to add/remove meta-tags to/from the page by highlighting/dehighlighting them.