Variant level CSV download

[bencap]

Adds a variant-level CSV download and replaces the score-set custom-download dialog with a shared column picker driven by the API's namespace-discovery endpoints. Requires the API-side GET /score-sets/{urn}/csv-namespaces, GET /variants/{urn}/csv-namespaces, and GET /variants/{urn}/csv. See VariantEffect/mavedb-api#804.

CSV column picker

• New use-csv-namespaces.ts composable and MvCsvColumnDialog.vue fetch a score set's or variant's available column namespaces and let the user choose which to include.
• Sections are grouped and labeled by the server (Measurements, Annotations, Clinical interpretation, Provenance) rather than maintained client-side, and are split by owning score set when a variant's calibrations span more than one.
• Initial selection follows the API's selectedByDefault flag, so a research-use-only or rangeless calibration is offered but must be opted into explicitly.
• Replaces the old hand-picked checkbox list (scores / counts / mappedHgvs / etc.), whose query params the API never actually read. Used in MvVariantPreview.vue's "Custom Data" dialog, ScoreSetDownloads.vue, and VariantScreen.vue.

Variant-level download

• VariantScreen.vue gains a "Download variant CSV" control backed by GET /variants/{urn}/csv, kept separate from the existing VA-Spec annotation downloads.
• use-variant-lookup.ts gains downloadVariantCsvFile and a shared downloadInProgressLabel.

Annotation-stream memory fix

• streamAnnotationsInto accumulated NDJSON chunks as decoded strings, then joined them, then built a Blob from the result — holding roughly five copies of the payload at once, enough to run the tab out of memory on a large pathogenicity-statement download. It now accumulates raw Uint8Array chunks, builds the Blob directly from them, and counts newline bytes for progress instead of decoding.
• A stream that delivers fewer lines than X-Total-Count now throws rather than silently saving a partial file.

Shared download indicator

• Per-feature annotatedDownloadInProgress / Progress state is replaced by a single fileDownloadLabel / fileDownloadProgress pair covering every download the composable offers (scores, counts, mapped variants, custom data, VA-Spec streams), via a withIndicator() wrapper that also blocks concurrent downloads.
• ScoreSetDownloads.vue renders one progress bar under the button row instead of one hung off the annotated-variants split button, and disables every download button while any download is in flight. Progress is indeterminate except for the VA-Spec streams, which count records against X-Total-Count.
• reportingFailure() surfaces a rejected download as a toast instead of an unhandled promise rejection.

Supporting changes

• getErrorResponse moves out of api/mavedb/index.ts into a new src/lib/errors.ts, joined by describeRequestError, which replaces the ad hoc extractErrorDetail in ScoreSetCalibrationsView.vue. All call sites now import from @/lib/errors.
• score-sets.ts and variants.ts switch their CSV requests from drop_na_columns and include_post_mapped_hgvs to drop_unused_hgvs_columns plus the namespace list, matching the API's parameter names.
• openapi.d.ts regenerated for the AvailableCsvNamespace and CsvNamespaceGroup schemas and the new endpoints.

Tests

Unit tests added for use-csv-namespaces, use-score-set-downloads, and lib/errors.

[coveralls]

coverage: 9.654% (+3.0%) from 6.656% — feature/bencap/variant-level-csv-download into release-2026.2.4.1