Reduce demo to 3 charts, fix back-button district name bug

Fixes the deep-link/back-button bug where the district name showed
"Unknown District" on return: App.jsx was passing the LEAID as a text
search query to searchDistricts() (a name search), which never matches a
numeric ID. Resolves it instead via fetchDistrictEstimates(leaid, ...) and
reads lea_name/state directly from the returned row - correct regardless
of how the page was reached (fresh load, refresh, or browser back/forward).

Cuts the demo from 6 charts to 3, per request: arrests over time (kept),
arrest rate by student group restructured into Female/Male box-and-whisker
panels (kept), and the posterior density ridge chart restructured from a
2x2 model-quadrant grid into a single selected model (dropdown, default
three-year + referral rate) with Female/Male ridge columns. Removes
DistrictVsNational, ModelDrawsComparison, and ExceedanceProbability
entirely, along with the student-group filter (no longer needed - the
remaining charts always show the full breakdown) and the national-rates
fetch/plumbing that only those removed charts used.

Also updates LoadingAnimation's copy and dedupes its STUDENT_GROUPS/
MODEL_QUADRANTS constants against the shared ones in useApi.js.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/App.jsx

@@ -4,7 +4,7 @@ import DistrictSearch from './components/DistrictSearch.jsx'
 import LoadingAnimation from './components/LoadingAnimation.jsx'
 import ChartPanel from './components/ChartPanel.jsx'
 import Footer from './components/Footer.jsx'
-import { searchDistricts } from './hooks/useApi.js'
+import { fetchDistrictEstimates } from './hooks/useApi.js'
 
 /**
  * CRDC Arrests API Demo App — main router.
@@ -21,18 +21,18 @@ export default function App() {
     const leaid = params.get('leaid')
     const stateParam = params.get('state')
     if (leaid && stateParam) {
-      // Deep link: fetch district name first, then go to loading.
+      // Deep link (including browser back/forward landing on this URL): resolve
+      // the district name via a real estimates row, keyed by LEAID. The previous
+      // version called searchDistricts(leaid, ...), a name/text search — passing
+      // an LEAID as search text never matches, so it always fell back to "Unknown
+      // District".
       setSelectedState(stateParam)
-      
-      // Fetch district name from API
-      searchDistricts(leaid, stateParam).then(results => {
-        const district = results?.find(d => d.leaid === leaid)
-        if (district) {
-          setDistrict(district)
-        } else {
-          // Fallback if district not found
-          setDistrict({ leaid, lea_name: 'Unknown District', state: stateParam })
-        }
+
+      fetchDistrictEstimates(leaid, { model: 'unified_m2_mod', year: '21-22' }).then(rows => {
+        const row = rows?.[0]
+        setDistrict(row
+          ? { leaid: row.leaid, lea_name: row.lea_name, state: row.state }
+          : { leaid, lea_name: 'Unknown District', state: stateParam })
         setStep('loading')
       }).catch(() => {
         // Fallback on error