Add BRC datasets to Google Datasets catalog

Add BRC datasets to the [Google Dataset Search](https://datasetsearch.research.google.com/) catalog so assemblies are discoverable from Google. This is done by embedding [schema.org Dataset](https://schema.org/Dataset) JSON-LD on the relevant pages — Google's crawler picks it up.

## Reference implementation

NCPI Dataset Catalog has already shipped this for studies. Mirror their pattern:

- Builder + types: [`app/utils/schemaOrg.ts`](https://github.com/NIH-NCPI/ncpi-dataset-catalog/blob/main/app/utils/schemaOrg.ts) — `SchemaDataset` interface and `buildStudyJsonLd()` factory.
- Render component: [`app/components/Detail/components/StudyJsonLd/studyJsonLd.tsx`](https://github.com/NIH-NCPI/ncpi-dataset-catalog/blob/main/app/components/Detail/components/StudyJsonLd/studyJsonLd.tsx) — wraps the JSON-LD in a `` inside `next/head`, with HTML escaping to prevent script injection.
- Page integration: [`pages/[entityListType]/[...params].tsx`](https://github.com/NIH-NCPI/ncpi-dataset-catalog/blob/main/pages/%5BentityListType%5D/%5B...params%5D.tsx) — mounted on the detail route only.
- Tests: [`app/utils/schemaOrg.test.ts`](https://github.com/NIH-NCPI/ncpi-dataset-catalog/blob/main/app/utils/schemaOrg.test.ts) — covers required fields, truncation, and conditional fields.

## Google Dataset required + recommended fields

Per [Google's Dataset structured data guidelines](https://developers.google.com/search/docs/appearance/structured-data/dataset):

**Required**
- `name` — descriptive title
- `description` — 50–5000 characters

**Recommended**
- `identifier`, `url`, `sameAs`
- `creator`, `funder`, `license`
- `distribution` (with `contentUrl`, `encodingFormat`)
- `keywords`, `variableMeasured`, `measurementTechnique`
- `spatialCoverage`, `temporalCoverage`
- `includedInDataCatalog`, `isAccessibleForFree`, `version`, `citation`

## Initial mapping — assembly (`BRCDataCatalogGenome`) → `Dataset`

Source entity at [`app/apis/catalog/brc-analytics-catalog/common/entities.ts`](app/apis/catalog/brc-analytics-catalog/common/entities.ts) (`BRCDataCatalogGenome`).

| schema.org field | Source / value |
| --- | --- |
| `@context` | `\"https://schema.org\"` |
| `@type` | `\"Dataset\"` |
| `name` | `${taxonomicLevelSpecies}${strainName ? \" — \" + strainName : \"\"} (${accession})` |
| `description` | Composed sentence: species + strain + accession + assembly level + chromosome/scaffold counts + length. Strip HTML, truncate to 5000 chars. |
| `identifier` | `[accession, ncbiTaxonomyId]` (NCBI assembly accession + taxonomy ID) |
| `url` | `${browserURL}/data/organisms/${ncbiTaxonomyId}/genomes/${accession}` (or whichever route resolves the assembly detail page) |
| `sameAs` | NCBI assembly URL: `https://www.ncbi.nlm.nih.gov/datasets/genome/${accession}/` |
| `includedInDataCatalog` | `{ \"@type\": \"DataCatalog\", name: \"BRC Analytics\", url: browserURL }` |
| `isAccessibleForFree` | `true` |
| `keywords` | `[priorityPathogenName, ...taxonomicGroup, taxonomicLevelKingdom, taxonomicLevelFamily, taxonomicLevelGenus, taxonomicLevelSpecies].filter(Boolean)` |
| `version` | `accession` version suffix (e.g. trailing `.1`/`.2`) if parseable |
| `distribution` | Build `DataDownload[]` from any of: `galaxyDatacacheUrl`, `geneModelUrl`, `ucscBrowserUrl` (when present). Set `encodingFormat` per source (`application/gzip`, `text/x-gff3`, `text/html`). |
| `variableMeasured` | Optional: `[\"chromosomes\", \"scaffoldCount\", \"scaffoldN50\", \"scaffoldL50\", \"gcPercent\", \"length\", \"coverage\"]` filtered to populated values, encoded as `PropertyValue` objects. |
| `creator` | Optional: `{ \"@type\": \"Organization\", name: \"BRC Analytics\" }` until per-assembly source attribution is available. |
| `license` | TBD — confirm with team (likely a permissive public-domain notice for the metadata). |

Open questions for `variableMeasured` / `creator` / `license` should be resolved before merge.

## Implementation steps

1. Add `app/utils/schemaOrg.ts` with `SchemaDataset` types and `buildAssemblyJsonLd(genome, browserURL)`.
2. Add `app/components/.../AssemblyJsonLd` component that renders the JSON-LD via `next/head` with the same HTML-escape helper as NCPI.
3. Mount the component on the assembly detail page (`pages/data/[entityListType]/[entityId]/index.tsx`).
4. Unit-test the builder: required fields present, description truncation, conditional fields omitted when source is null.
5. Validate output against [Google's Rich Results Test](https://search.google.com/test/rich-results) and [Schema Markup Validator](https://validator.schema.org/) for a few representative assemblies (high-priority pathogen, eukaryote, virus).
6. Once shipped, request indexing via Google Search Console and confirm dataset pages start appearing in Google Dataset Search.

## Out of scope (follow-ups)

- Mapping for organism pages (`BRCDataCatalogOrganism`).
- Sitemap entries for assembly detail pages if not already present.