Validate facets against base authorization, not active drilldowns

Observation (2026-09-04, code review of theft PR #723 / COR-3895): when URL filter values are normalized against the currently selected team/user drilldown, a valid organization-wide value with zero rows in that drilldown can normalize to an empty selection and accidentally behave as “All.” Build facet options and validate requested values against the user’s base authorized visibility scope, then apply team/user drilldowns only to the result query. This preserves zero-result intersections without leaking inaccessible values. The same review also confirmed an efficient shape: one authorization-scoped CASE/COUNT/GROUP BY facet query returning only vocabulary rows, plus a parameterized SQL IN predicate before pagination/hydration; no organization-load transfer to application memory.