frontend: date range picker on Incidents and Archive; fix Archive paging

Incidents and Archive get a from/to date range (native date inputs,
local-day bounds). Incidents filters in the Firestore query; Archive
passes date_from/date_to to GET /calls/search, which applies them as a
started_at range — both ride the existing org_id/started_at index.

Also fixes /calls/search and /calls/eval-queue paging: the cursor went to
Firestore as a raw ISO string against a timestamp field, which compares
by type rather than time, so "Load more" re-read the first page. Cursor
and range bounds are now parsed to datetimes (400 on garbage).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/app/calls/page.tsx

@@ -24,6 +24,7 @@ import { Button } from "@/components/ui/Button";
 import { EmptyState, ErrorBanner } from "@/components/ui/EmptyState";
 import { SkeletonCard } from "@/components/ui/Skeleton";
 import { MachineOutputNotice } from "@/components/ui/MachineOutputNotice";
+import { DateRange, dayStart, dayEnd } from "@/components/ui/DateRange";
 
 type LinkFilter = "any" | "orphan" | "linked";
 type TranscriptFilter = "any" | "yes" | "no";
@@ -239,6 +240,8 @@ export default function ArchivePage() {
   const [systemId, setSystemId] = useState("");
   const [q, setQ] = useState("");
   const [submittedQ, setSubmittedQ] = useState("");
+  const [dateFrom, setDateFrom] = useState("");
+  const [dateTo, setDateTo] = useState("");
 
   useEffect(() => {
     if (!authLoading && !canView) router.replace("/");
@@ -256,6 +259,8 @@ export default function ArchivePage() {
           transcript,
           system_id: systemId || undefined,
           q: submittedQ || undefined,
+          date_from: dayStart(dateFrom)?.toISOString(),
+          date_to: dayEnd(dateTo)?.toISOString(),
         });
         setCalls((prev) => (append ? [...prev, ...res.calls] : res.calls));
         setCursor(res.next_cursor);
@@ -266,7 +271,7 @@ export default function ArchivePage() {
         setLoading(false);
       }
     },
-    [link, transcript, systemId, submittedQ],
+    [link, transcript, systemId, submittedQ, dateFrom, dateTo],
   );
 
   // Reload from the top whenever a filter changes.
@@ -335,6 +340,8 @@ export default function ArchivePage() {
           ))}
         </select>
 
+        <DateRange from={dateFrom} to={dateTo} onChange={(f, t) => { setDateFrom(f); setDateTo(t); }} />
+
         <form
           onSubmit={(e) => { e.preventDefault(); setSubmittedQ(q.trim()); }}
           className="flex items-center gap-2 ml-auto"