Issue #3613117: Dashboard terminology and filter placement cleanup

Closes #3613117

Renames "Editor" to "User" in the per-editor dashboard's page title, menu item, and table heading, since the aggregation is per Drupal user account, not a role.

Moves the month/year filter above the KPI cards on both dashboards, since everything below it (KPIs, chart, table) is scoped by that selection. Wraps the filter in a <fieldset>/<legend> instead of bare labels, so screen readers associate the "Reporting period" grouping with its controls.

Out of scope for #3613099 (charts/blocks fix, already merged); split out per review discussion since this is pure copy/layout, unrelated to the caching architecture.

Tests: existing 241 tests unaffected (no test asserts the old title/heading strings), full suite green.