Adds a zoom action that narrows the visible timeline range to the current
selection so the user can drill from year-level back into month-level
density. Zoom state lives in the URL (zoomFrom / zoomTo) so it survives
reload and is shareable.
- New `clipBucketsToRange(buckets, from, to)` helper applied before the
>240-month year-aggregate decision, so a zoomed window flips back to
month bars automatically when the clip narrows the range enough.
- `TimelineDensityFilter` gains `zoomFrom`, `zoomTo`, and `onzoomchange`
props. Zoom button shown only when a selection exists and we aren't
already zoomed; reset-zoom shown only when zoomed. Both placed in a
shared right-edge action cluster alongside the × clear button.
- `+page.ts` reads zoomFrom/zoomTo from the URL and forwards them as
props. `+page.svelte` extends FilterSnapshot + buildSearchParams, and
triggerSearch accepts an optional zoom override so the onzoomchange
callback can write the new pair (or clear them) atomically.
- 7 new component tests + 2 new page-integration tests cover the
visibility rules and URL writes.
- 4 new unit tests for `clipBucketsToRange`.
- 3 new i18n keys (zoom in / zoom reset / drag aria-live) across de/en/es.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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