fix: limit daily chart to last 15 days and sort sessions newest-first

Slice daily chart to the most recent 15 days to keep it readable.
Reverse session sort order within each day so the latest entries
appear at the top.

Author: 658jjh

js/components/charts.js

@@ -132,7 +132,7 @@ function buildDailyChart(allSessions) {
         dailyBySource[s.date][s.source] = (dailyBySource[s.date][s.source] || 0) + s.cost;
         allSourcesSet.add(s.source);
     });
-    const chartDays = Object.keys(dailyBySource).sort();
+    const chartDays = Object.keys(dailyBySource).sort().slice(-15);
     const allSources = Array.from(allSourcesSet);
 
     const canvas = document.getElementById('dailyChart');

js/components/sessions-table.js

@@ -209,7 +209,7 @@ export function buildDayDetail(date, sessions) {
                 <th>Time</th><th>Source</th><th>Model</th>
                 <th>Input</th><th>Output</th><th>Cache R</th><th>Cache W</th><th style="text-align:right">Cost</th>
             </tr></thead><tbody>`;
-    sessions.sort((a, b) => (a.time || '').localeCompare(b.time || ''));
+    sessions.sort((a, b) => (b.time || '').localeCompare(a.time || ''));
     for (const s of sessions) {
         const mi = getModelInfo(s.model);
         const sc = sourceClass(s.source);