feat(ux): implement comprehensive UX audit fixes across all pages

Addresses 28 issues identified in UX audit (P0–P3 severity):

P0 — Critical:
- Fix compare URL sharing: seed ComparisonContext from SSR initialData
  when localStorage is empty, making /compare?urns=... links shareable
- Remove permanently broken "Avg. Scaled Score" column from school
  detail historical data table

P1 — High priority:
- Add radius selector (0.5–10 mi) to postcode search in FilterBar
- Make Add to Compare a toggle (remove) on SchoolCards
- Hide hero title/description once a search is active
- Show school count + quick-search prompts on empty landing page
- Compare empty state opens in-page school search modal directly
- Remove URN from school detail header (irrelevant to end users)
- Move map above performance chart in school detail page
- Add ← Back navigation to school detail page
- Add sort controls to search results (RWM%, distance, A–Z)
- Show metric descriptions below metric selector
- Expand ComparisonToast to list school names with per-school remove
- Add progress score explainer (0 = national average) throughout

P2 — Medium:
- Remove console.log statements from ComparisonView
- Colour-code comparison school cards to match chart line colours
- Replace plain loading text with LoadingSkeleton in ComparisonView
- Rankings empty state uses shared EmptyState component
- Rankings year filter shows actual year e.g. "2023 (Latest)"
- Rankings subtitle shows top-N count
- Add View link alongside Add button in rankings table
- Remove placeholder Privacy Policy / Terms links from footer
- Replace untappable 10px info icons with visible metric hint text
- Show active filter chips in search results header

P3 — Polish:
- Remove redundant "Home" nav link (logo already links home)
- Add / and Ctrl+K keyboard shortcut to focus search input
- Add Share button to compare page (copies URL to clipboard)

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

nextjs-app/components/SchoolDetailView.tsx

@@ -5,6 +5,7 @@
 
 'use client';
 
+import { useRouter } from 'next/navigation';
 import { useComparison } from '@/hooks/useComparison';
 import { PerformanceChart } from './PerformanceChart';
 import { SchoolMap } from './SchoolMap';
@@ -19,6 +20,7 @@ interface SchoolDetailViewProps {
 }
 
 export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: SchoolDetailViewProps) {
+  const router = useRouter();
   const { addSchool, removeSchool, isSelected } = useComparison();
   const isInComparison = isSelected(schoolInfo.urn);
 
@@ -36,6 +38,11 @@ export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: School
 
   return (
     <div className={styles.container}>
+      {/* Back Navigation */}
+      <div className={styles.backNav}>
+        <button onClick={() => router.back()} className={styles.backButton}>← Back</button>
+      </div>
+
       {/* Header Section */}
       <header className={styles.header}>
         <div className={styles.headerContent}>
@@ -52,9 +59,6 @@ export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: School
                   {schoolInfo.school_type}
                 </span>
               )}
-              <span className={styles.metaItem}>
-                URN: {schoolInfo.urn}
-              </span>
             </div>
             {schoolInfo.address && (
               <p className={styles.address}>
@@ -137,6 +141,23 @@ export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: School
             )}
 
           </div>
+          {(latestResults.reading_progress !== null || latestResults.writing_progress !== null || latestResults.maths_progress !== null) && (
+            <p className={styles.progressNote}>Progress scores: 0 = national average. Positive = above average, negative = below average.</p>
+          )}
+        </section>
+      )}
+
+      {/* Map */}
+      {schoolInfo.latitude && schoolInfo.longitude && (
+        <section className={styles.mapSection}>
+          <h2 className={styles.sectionTitle}>Location</h2>
+          <div className={styles.mapContainer}>
+            <SchoolMap
+              schools={[schoolInfo]}
+              center={[schoolInfo.latitude, schoolInfo.longitude]}
+              zoom={15}
+            />
+          </div>
         </section>
       )}
 
@@ -269,20 +290,6 @@ export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: School
         </section>
       )}
 
-      {/* Map */}
-      {schoolInfo.latitude && schoolInfo.longitude && (
-        <section className={styles.mapSection}>
-          <h2 className={styles.sectionTitle}>Location</h2>
-          <div className={styles.mapContainer}>
-            <SchoolMap
-              schools={[schoolInfo]}
-              center={[schoolInfo.latitude, schoolInfo.longitude]}
-              zoom={15}
-            />
-          </div>
-        </section>
-      )}
-
       {/* All Years Data Table */}
       {yearlyData.length > 0 && (
         <section className={styles.historySection}>
@@ -297,7 +304,6 @@ export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: School
                   <th>Reading Progress</th>
                   <th>Writing Progress</th>
                   <th>Maths Progress</th>
-                  <th>Avg. Scaled Score</th>
                 </tr>
               </thead>
               <tbody>
@@ -309,7 +315,6 @@ export function SchoolDetailView({ schoolInfo, yearlyData, absenceData }: School
                     <td>{result.reading_progress !== null ? formatProgress(result.reading_progress) : '-'}</td>
                     <td>{result.writing_progress !== null ? formatProgress(result.writing_progress) : '-'}</td>
                     <td>{result.maths_progress !== null ? formatProgress(result.maths_progress) : '-'}</td>
-                    <td>-</td>
                   </tr>
                 ))}
               </tbody>