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-c2-core/tests/test_calls_parse_ts.py

@@ -0,0 +1,35 @@
+"""calls._parse_ts — cursor/date bounds must reach Firestore as datetimes.
+
+A raw ISO string compared against a timestamp field sorts by type, not time,
+which made the Archive's "Load more" return the first page again.
+"""
+from datetime import datetime, timezone
+
+import pytest
+from fastapi import HTTPException
+
+from app.routers.calls import _parse_ts
+
+
+def test_empty_is_none():
+    assert _parse_ts(None, "cursor") is None
+    assert _parse_ts("", "cursor") is None
+
+
+def test_z_suffix_parses_as_utc():
+    assert _parse_ts("2026-09-20T12:00:00Z", "date_from") == datetime(2026, 9, 20, 12, tzinfo=timezone.utc)
+
+
+def test_naive_is_assumed_utc():
+    assert _parse_ts("2026-09-20T12:00:00", "date_to").tzinfo == timezone.utc
+
+
+def test_round_trips_isoformat_cursor():
+    dt = datetime(2026, 9, 20, 12, 30, 5, 123456, tzinfo=timezone.utc)
+    assert _parse_ts(dt.isoformat(), "cursor") == dt
+
+
+def test_garbage_is_400():
+    with pytest.raises(HTTPException) as exc:
+        _parse_ts("yesterday", "date_from")
+    assert exc.value.status_code == 400