fix(search): offer every phase while a phase filter is applied

The phase select read its options from the result-scoped filters, which
the backend computes after applying the phase filter. With secondary
chosen only secondary and all-through were offered, so switching to
primary meant going back to "Any phase" first. Read the global phase
list instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

nextjs-app/components/FilterBar.tsx

@@ -295,7 +295,10 @@ export function FilterBar({
   const laOptions =
     resultFilters?.local_authorities ?? filters.local_authorities;
   const typeOptions = resultFilters?.school_types ?? filters.school_types;
-  const phaseOptions = resultFilters?.phases ?? filters.phases ?? [];
+  // Phase is the exception: always the full list. The result set has already
+  // been narrowed by the phase filter, so scoping to it would leave only the
+  // chosen phase on offer and switching phase would need "Any phase" first.
+  const phaseOptions = filters.phases ?? [];
   const genderOptions = resultFilters?.genders ?? filters.genders ?? [];
   const admissionsPolicyOptions =
     resultFilters?.admissions_policies ?? filters.admissions_policies ?? [];