[Feature] Better <title/> for users and tags Hypothesis pages

**Describe the feature**
It'd be nice to have the name of the user or the tag displayed as part of the `</head>` element.

That way, when bookmarking an Hypothesis user page or a specific tag, the title of the annotation would contain more precise information.

For example:

```html
<title>Hypothesis/users/kael
```
```html
Hypothesis/tag/RDF
```

This looks a bit cosmetic, but would really be visually useful when bookmarking such pages.

Currently, only `Hypothesis` is displayed as the bookmark title, so it's not possible to distinguish bookmarks without hovering over their URI.

The issue does not name files or tests. Locate the templates or entry points for user and tag pages, then inspect how the document title is set. Done means those pages include the user or tag name in the title so bookmarks can be distinguished.

Written by the indexing model from the issue text.