Mounts the timeline above the result count, hidden on mobile via
\`hidden sm:block\` (defense-in-depth — +page.ts already gates the fetch).
The component's onchange callback updates local from/to and triggers
the existing search reload, so timeline selection composes with the
SearchFilterBar's other filters via AND semantics for free.
3 new page-level integration tests cover: widget renders when density
present, hides when null, and bar click navigates with correct
from/to URL params.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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