fix(tags): Set consistent titles for tags with description pages

Right now for some tag `my-tag` a tag page with title `Tag: my-tag` is
generated.
However if you create a page `tags/my-tag.md` to add a description the
page will have the title `my-tag` by default.

Set the tag page title to have the `Tag: ` prefix if the tag page does
not have a custom title for consistency between tags with and without
descriptions.

quartz/plugins/emitters/tagPage.tsx

@@ -105,6 +105,9 @@ export const TagPage: QuartzEmitterPlugin<Partial<TagPageOptions>> = (userOpts)
           const tag = slug.slice("tags/".length)
           if (tags.has(tag)) {
             tagDescriptions[tag] = [tree, file]
+            if (file.data.frontmatter?.title === tag) {
+              file.data.frontmatter.title = `${i18n(cfg.locale).pages.tagContent.tag}: ${tag}`
+            }
           }
         }
       }