gotoFilter() built a brand-new URLSearchParams containing only the
clicked chart segment's filter keys, discarding every other active
filter (search text, date range, saved-filter selection, etc.) on
navigation. Now merges the segment's filter into the current
location.search, same fix approach already applied to #22.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MGDKHiU5RJdo3dqQUDow3X