Make filters harder to break

Filters that silently matched nothing were hard to notice and easy to reintroduce. Alongside the fix, we tightened how filters are built and tested.

• Rebuilt the filter search syntax so quoted values survive intact, covered by an exhaustive test suite
• Made a misconfigured filter fail immediately instead of quietly rendering nothing
• Fixed long filter names pushing their counts out of column, and shortened them with the full name on hover