feat: global time range context with custom date picker

Lift time range state into a shared React context so the selected
range persists across page navigation and browser refreshes
(localStorage). Add a "Custom" option with a popover date picker
that lets users specify arbitrary start/end dates. All preset end
times now use endOf("day") (23:59:59) instead of the current moment.

app/aggregation/page.tsx

@@ -4,7 +4,8 @@ import { useEffect, useState, useCallback } from "react";
 import { motion } from "motion/react";
 import { Users, Calendar, Hash, Zap, ArrowUpDown, ArrowDown, ArrowUp } from "lucide-react";
 import { TimeRangeSelector } from "@/components/TimeRangeSelector";
-import { type TimeRange, getTimeRange, buildQuery, formatNumber, formatTokens } from "@/lib/utils";
+import { buildQuery, formatNumber, formatTokens } from "@/lib/utils";
+import { useTimeRange } from "@/lib/time-range-context";
 import { useI18n } from "@/lib/i18n";
 
 interface AggItem {
@@ -16,7 +17,7 @@ type SortKey = "total_tokens" | "calls" | "prompt_tokens" | "completion_tokens";
 
 export default function AggregationPage() {
   const { t } = useI18n();
-  const [range, setRange] = useState<TimeRange>("30d");
+  const { getEffectiveRange } = useTimeRange();
   const [data, setData] = useState<AggItem[]>([]);
   const [loading, setLoading] = useState(true);
   const [sortKey, setSortKey] = useState<SortKey>("total_tokens");
@@ -24,11 +25,11 @@ export default function AggregationPage() {
 
   const fetchData = useCallback(async () => {
     setLoading(true);
-    const { start, end } = getTimeRange(range);
+    const { start, end } = getEffectiveRange();
     const res = await fetch(buildQuery("/api/aggregation", { start, end }));
     setData(await res.json());
     setLoading(false);
-  }, [range]);
+  }, [getEffectiveRange]);
 
   useEffect(() => { fetchData(); }, [fetchData]);
 
@@ -68,7 +69,7 @@ export default function AggregationPage() {
           <Users className="h-5 w-5" style={{ color: "var(--accent)", opacity: 0.6 }} />
           <h1 className="text-2xl font-bold gradient-text">{t("agg.title")}</h1>
         </motion.div>
-        <TimeRangeSelector value={range} onChange={setRange} />
+        <TimeRangeSelector />
       </div>
 
       {!loading && data.length > 0 && (