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/RankingsView.tsx

@@ -9,6 +9,7 @@ import { useRouter, usePathname, useSearchParams } from 'next/navigation';
 import { useComparison } from '@/hooks/useComparison';
 import type { RankingEntry, Filters, MetricDefinition } from '@/lib/types';
 import { formatPercentage, formatProgress } from '@/lib/utils';
+import { EmptyState } from './EmptyState';
 import styles from './RankingsView.module.css';
 
 interface RankingsViewProps {
@@ -83,9 +84,17 @@ export function RankingsView({
         <h1>School Rankings</h1>
         <p className={styles.subtitle}>
           Top-performing schools by {metricLabel.toLowerCase()}
+          {!selectedArea && <span className={styles.limitNote}> — showing top {rankings.length}</span>}
         </p>
       </header>
 
+      {currentMetricDef?.description && (
+        <p className={styles.metricDescription}>{currentMetricDef.description}</p>
+      )}
+      {isProgressScore && (
+        <p className={styles.progressHint}>Progress scores: 0 = national average. Positive = above average.</p>
+      )}
+
       {/* Filters */}
       <section className={styles.filters}>
         <div className={styles.filterGroup}>
@@ -170,7 +179,9 @@ export function RankingsView({
             onChange={(e) => handleYearChange(e.target.value)}
             className={styles.filterSelect}
           >
-            <option value="">Latest</option>
+            <option value="">
+              {filters.years.length > 0 ? `${Math.max(...filters.years)} (Latest)` : 'Latest'}
+            </option>
             {filters.years.map((year) => (
               <option key={year} value={year}>
                 {year}
@@ -183,9 +194,14 @@ export function RankingsView({
       {/* Rankings Table */}
       <section className={styles.rankingsSection}>
         {rankings.length === 0 ? (
-          <div className={styles.noResults}>
-            <p>No rankings available for the selected filters.</p>
-          </div>
+          <EmptyState
+            title="No rankings found"
+            message="Try selecting a different metric, area, or year."
+            action={{
+              label: 'Clear filters',
+              onClick: () => router.push(pathname),
+            }}
+          />
         ) : (
           <div className={styles.tableWrapper}>
             <table className={styles.rankingsTable}>
@@ -242,6 +258,7 @@ export function RankingsView({
                         <strong>{displayValue}</strong>
                       </td>
                       <td className={styles.actionCell}>
+                        <a href={`/school/${ranking.urn}`} className={styles.viewButton}>View</a>
                         <button
                           onClick={() => handleAddToCompare(ranking)}
                           disabled={alreadyInComparison}