Enhanced Taxonomy Manager 2.2.1

Adds analytics cards to the dashboard.

The dashboard opened with two numbers and a table. It now opens with
twelve metrics covering the shape and health of the site's taxonomy.

Structure: vocabularies, total terms, root terms, terms with children
with the average number of children each, leaf terms with their share of
the total, the deepest term and the level it sits at, the largest
vocabulary, and terms filed under more than one parent.

Health: unpublished terms, orphaned terms whose parent no longer exists,
duplicate names within a vocabulary, and terms changed in the last week.
Each turns amber or red only when there is something to act on, and
links through to the vocabulary holding the most of them with the
relevant sidebar panel already open. Colour is a reinforcement rather
than the signal — every card states its number and label regardless.

The tree now reads a ?panel= query parameter on arrival and opens the
matching sidebar panel, which is what makes those links land somewhere
useful.

Every figure comes from aggregate queries over the term and parent
tables, so the cost does not grow with the number of terms. The
per-vocabulary loop that builds the table below used to issue two
counting queries per vocabulary and now reads the same aggregates, so
the page went from 45 queries to 27 on an eight-vocabulary site while
gaining all of the above.

No database updates are required.