feat(website): collection tagging UI

[fhennig]

Summary

Add tagging UI to collections on the frontend: type definitions, form input, detail view, and list filtering.

Depends on: #1265

Type changes (Collection.ts)

• Add tags: string[] to Collection and CollectionSummary.
• Add tags: string[] (default []) to CollectionRequest schema.
• Add tags: string[] | undefined to CollectionUpdate schema (undefined = no change).

CollectionForm (CollectionForm.tsx)

Multi-tag input field:

• User types a tag and confirms with Enter or comma → tag appears as a removable chip.
• Tags are lowercased on input (mirrors backend normalisation).
• Submitted as the tags array in the request body.

CollectionDetail (CollectionDetail.tsx)

Display the collection's tags as chips in the metadata section (alongside name, organism, description).

Collections list page

• Add a tag filter control (multi-tag chip input or multi-select).
• When one or more tags are selected, pass them as ?tags=… query params to the API (AND semantics — all selected tags must be present).
• Update getCollections.ts to accept and forward a tags?: string[] parameter.