Add a dashboard search box to the landing page

[ckrew]

Filters the landing page by dashboard name and description as you type. Names and descriptions are matched differently on purpose.

A name is matched as a plain substring of the whole query, stopwords included, so "guat" finds "Guatemala Hands On 1" and a dashboard actually called "The Basin" stays findable by typing "the".

A description is matched by its significant words only, with common English function words dropped from the query. Requiring "the" to appear would surface nearly every dashboard in the app, which is noise rather than a filter. A query made up entirely of stopwords therefore leaves no description terms and falls back to name matching alone -- the case that makes the feature worth having.

Two supporting choices: query tokens match inside longer words, so "flood" finds "flooding"; and both sides are NFD-normalized before comparison, so "clasificacion" finds "Clasificación".

The matcher lives in its own module and is pure, so it is tested directly rather than only through the rendered page. The box hides itself when there are no dashboards to search, reports "n of m dashboards" while filtering, offers a clear button, and shows a no-matches message instead of an empty page. The New Dashboard tile is hidden while a query is active, since it is not a dashboard and would read as a match.

No backend change: name and description are already in the dashboard metadata.