fix(years): format academic years as 2016/17 across all views, remove legacy frontend and data

Apply formatAcademicYear to all year displays in ComparisonChart, ComparisonView,
PerformanceChart, and RankingsView. Remove old vanilla JS frontend and CSV data
directory — both superseded by the Next.js app and Meltano pipeline.

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

nextjs-app/components/PerformanceChart.tsx

@@ -18,6 +18,7 @@ import {
   ChartOptions,
 } from 'chart.js';
 import type { SchoolResult } from '@/lib/types';
+import { formatAcademicYear } from '@/lib/utils';
 import styles from './PerformanceChart.module.css';
 
 // Register Chart.js components
@@ -40,11 +41,7 @@ interface PerformanceChartProps {
 export function PerformanceChart({ data, schoolName, isSecondary = false }: PerformanceChartProps) {
   // Sort data by year
   const sortedData = [...data].sort((a, b) => a.year - b.year);
-  const formatYear = (y: number) => {
-    const s = y.toString();
-    return s.length === 6 ? `${s.slice(0, 4)}/${s.slice(4)}` : s;
-  };
-  const years = sortedData.map(d => formatYear(d.year));
+  const years = sortedData.map(d => formatAcademicYear(d.year));
 
   // Prepare datasets — phase-aware
   const datasets = isSecondary ? [