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/lib/c2api.ts

@@ -82,6 +82,8 @@ export const c2api = {
     link?: "any" | "orphan" | "linked";
     transcript?: "any" | "yes" | "no";
     q?: string;
+    date_from?: string;
+    date_to?: string;
   }) => {
     const qs = new URLSearchParams();
     for (const [k, v] of Object.entries(params)) {