refactor(phase): merge KS2+KS4 into fact_performance, fix all phase inconsistencies

Root cause: the UNION ALL query in data_loader.py produced two rows per
all-through school per year (one KS2, one KS4), with drop_duplicates()
silently discarding the KS4 row. Fixes:

- New dbt mart `fact_performance`: FULL OUTER JOIN of fact_ks2_performance
  and fact_ks4_performance on (urn, year). One row per school per year.
  All-through schools have both KS2 and KS4 columns populated.
- data_loader.py: replace 175-line UNION ALL with a simple JOIN to
  fact_performance. No more duplicate rows or drop_duplicates needed.
- sync_typesense.py: single LATERAL JOIN to fact_performance instead of
  two separate KS2/KS4 joins.
- app.py: remove drop_duplicates (no longer needed); add PHASE_GROUPS
  constant so all-through/middle schools appear in primary and secondary
  filter results (were previously invisible to both); scope result_filters
  gender/admissions_policies to secondary schools only.
- HomeView.tsx: isSecondaryView is now majority-based (not "any secondary")
  and isMixedView shows both sort option sets for mixed result sets.
- school/[slug]/page.tsx: all-through schools route to SchoolDetailView
  (renders both SATs + GCSE sections) instead of SecondarySchoolDetailView
  (KS4-only). Dedicated SEO metadata for all-through schools.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nextjs-app/components/HomeView.tsx

@@ -45,8 +45,11 @@ export function HomeView({ initialSchools, filters, totalSchools }: HomeViewProp
   const isLocationSearch = !!searchParams.get('postcode');
   const isSearchActive = !!(hasSearch || searchParams.get('local_authority') || searchParams.get('school_type'));
   const currentPhase = searchParams.get('phase') || '';
-  const hasSecondaryResults = allSchools.some(s => s.attainment_8_score != null);
-  const isSecondaryView = currentPhase.toLowerCase().includes('secondary') || hasSecondaryResults;
+  const secondaryCount = allSchools.filter(s => s.attainment_8_score != null).length;
+  const primaryCount = allSchools.filter(s => s.rwm_expected_pct != null).length;
+  const isSecondaryView = currentPhase.toLowerCase().includes('secondary')
+    || (!currentPhase && secondaryCount > primaryCount);
+  const isMixedView = primaryCount > 0 && secondaryCount > 0 && !currentPhase;
 
   // Reset pagination state when search params change
   useEffect(() => {
@@ -79,13 +82,13 @@ export function HomeView({ initialSchools, filters, totalSchools }: HomeViewProp
       .finally(() => setIsLoadingMap(false));
   }, [resultsView, searchParams]);
 
-  // Fetch LA averages when secondary schools are visible
+  // Fetch LA averages when secondary or mixed schools are visible
   useEffect(() => {
-    if (!isSecondaryView) return;
+    if (!isSecondaryView && !isMixedView) return;
     fetchLAaverages({ cache: 'force-cache' })
       .then(data => setLaAverages(data.secondary.attainment_8_by_la))
       .catch(() => {});
-  }, [isSecondaryView]);
+  }, [isSecondaryView, isMixedView]);
 
   const handleLoadMore = async () => {
     if (isLoadingMore || !hasMore) return;
@@ -209,10 +212,10 @@ export function HomeView({ initialSchools, filters, totalSchools }: HomeViewProp
                   className={styles.sortSelect}
                 >
                   <option value="default">Sort: Relevance</option>
-                  {!isSecondaryView && <option value="rwm_desc">Highest R, W &amp; M %</option>}
-                  {!isSecondaryView && <option value="rwm_asc">Lowest R, W &amp; M %</option>}
-                  {isSecondaryView && <option value="att8_desc">Highest Attainment 8</option>}
-                  {isSecondaryView && <option value="att8_asc">Lowest Attainment 8</option>}
+                  {(!isSecondaryView || isMixedView) && <option value="rwm_desc">Highest R, W &amp; M %</option>}
+                  {(!isSecondaryView || isMixedView) && <option value="rwm_asc">Lowest R, W &amp; M %</option>}
+                  {(isSecondaryView || isMixedView) && <option value="att8_desc">Highest Attainment 8</option>}
+                  {(isSecondaryView || isMixedView) && <option value="att8_asc">Lowest Attainment 8</option>}
                   {isLocationSearch && <option value="distance">Nearest first</option>}
                   <option value="name_asc">Name A–Z</option>
                 </select>