feat(charts): show actual dates in trend chart tooltips

Replace opaque W1/D1/month abbreviation tooltip titles with human-readable
period labels (e.g. "Week 1 · 1 Apr – 7 Apr", "1 April 2025", "April 2025")
in both Dashboard and Comparison trend charts.

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

src/components/Dashboard.tsx

@@ -88,7 +88,7 @@ export default function DashboardDemo({ data, seasons: _seasons, includeVAT, set
     return rows.reduce((s,r) => s + parseFloat(String((r as any)[f[m]]||0)), 0);
   }, [revenueField]);
 
-  const trendData = useMemo(() => {
+  const trendResult = useMemo(() => {
     const group = (rows: MuseumRecord[], ps: string) => {
       const s = new Date(ps); const acc: Record<number, MuseumRecord[]> = {};
       rows.forEach(r => {
@@ -102,18 +102,37 @@ export default function DashboardDemo({ data, seasons: _seasons, includeVAT, set
     };
     const pg = group(prevData, prevStart), cg = group(filteredData, start);
     const maxK = Math.max(...Object.keys(pg).map(Number), ...Object.keys(cg).map(Number), 1);
+    const s0 = new Date(start);
+    const fmt = (d: Date) => d.toLocaleDateString('en-GB', { day: 'numeric', month: 'short' });
     const labels = Array.from({length:maxK}, (_,i) =>
-      gran==='week' ? `W${i+1}` : gran==='month' ? L.monthShort[(new Date(start).getMonth()+i)%12] : `D${i+1}`
+      gran==='week' ? `W${i+1}` : gran==='month' ? L.monthShort[(s0.getMonth()+i)%12] : `D${i+1}`
     );
+    const tooltipLabels = Array.from({length:maxK}, (_,i) => {
+      if (gran==='week') {
+        const ws = new Date(s0.getTime() + i * 7 * 86400000);
+        const we = new Date(s0.getTime() + (i+1) * 7 * 86400000 - 86400000);
+        return `Week ${i+1}  ·  ${fmt(ws)} – ${fmt(we)}`;
+      }
+      if (gran==='month') {
+        const ms = new Date(s0.getFullYear(), s0.getMonth() + i, 1);
+        return ms.toLocaleDateString('en-GB', { month: 'long', year: 'numeric' });
+      }
+      const ds = new Date(s0.getTime() + i * 86400000);
+      return ds.toLocaleDateString('en-GB', { day: 'numeric', month: 'long', year: 'numeric' });
+    });
     const prevYear = parseInt(start.slice(0,4))-1;
     return {
-      labels,
-      datasets: [
-        { label:`${prevYear}`, data:labels.map((_,i) => pg[i+1]||0), borderColor:chartColors.muted, backgroundColor:'transparent', borderWidth:1.5, tension:0.4, pointRadius:0, borderDash:[4,3] },
-        { label:start.slice(0,4), data:labels.map((_,i) => cg[i+1]||0), borderColor:chartColors.primary, backgroundColor:chartColors.primary+'18', borderWidth:2.5, tension:0.4, fill:true, pointRadius:gran==='week'?3:1, pointBackgroundColor:chartColors.primary },
-      ]
+      tooltipLabels,
+      data: {
+        labels,
+        datasets: [
+          { label:`${prevYear}`, data:labels.map((_,i) => pg[i+1]||0), borderColor:chartColors.muted, backgroundColor:'transparent', borderWidth:1.5, tension:0.4, pointRadius:0, borderDash:[4,3] },
+          { label:start.slice(0,4), data:labels.map((_,i) => cg[i+1]||0), borderColor:chartColors.primary, backgroundColor:chartColors.primary+'18', borderWidth:2.5, tension:0.4, fill:true, pointRadius:gran==='week'?3:1, pointBackgroundColor:chartColors.primary },
+        ]
+      }
     };
   }, [filteredData, prevData, prevStart, start, metric, gran, getVal, L]);
+  const trendData = trendResult.data;
 
   const museumData = useMemo(() => {
     const g = groupByMuseum(filteredData, includeVAT);
@@ -172,6 +191,19 @@ export default function DashboardDemo({ data, seasons: _seasons, includeVAT, set
     const barNoLegend: any  = { ...chartOpts, plugins:{ ...chartOpts.plugins, legend:{ display:false } } };
     return { chartOpts, barHorizOpts, barNoLegend };
   }, [baseOpts]);
+  const trendOpts: any = useMemo(() => ({
+    ...chartOpts,
+    plugins: {
+      ...chartOpts.plugins,
+      tooltip: {
+        ...chartOpts.plugins.tooltip,
+        callbacks: {
+          title: (items: any[]) => trendResult.tooltipLabels[items[0]?.dataIndex] ?? items[0]?.label,
+        }
+      }
+    }
+  }), [chartOpts, trendResult.tooltipLabels]);
+
   const pieOptions: any = useMemo(() => ({
     responsive: true, maintainAspectRatio: false,
     plugins: {
@@ -250,7 +282,7 @@ export default function DashboardDemo({ data, seasons: _seasons, includeVAT, set
               {granOpts.map(o => <button key={o.value} type="button" aria-pressed={gran===o.value} className={`alt-ctrl${gran===o.value?' alt-ctrl-on':''}`} onClick={() => setGran(o.value)}>{o.label}</button>)}
             </div>
           </div>
-          <div className="alt-chart-wrap alt-chart-wrap--tall"><Line data={trendData} options={chartOpts} /></div>
+          <div className="alt-chart-wrap alt-chart-wrap--tall"><Line data={trendData} options={trendOpts} /></div>
         </div>
 
         <div className="alt-chart-card">