fix(web): artifact rows match @corbits/artifacts 0.2.1 (no ownerName) (CL-8515)

[TheGreatAxios]

Summary

• `@corbits/artifacts` 0.2.1 dropped `ownerName` from serialized artifact rows and added `metadata` (opaque, nullable object); the web schemas still required `ownerName`, so every artifact list/detail response failed arktype parsing and `/artifacts` showed "Couldn't load your artifacts".
• Removed `ownerName` from `ArtifactListItemSchema`/`ArtifactRowSchema` (apps/web/src/api.ts) and added `metadata` to match the library's serialized row shape; removed `ownerName` from every consumer (artifact-summary, library-artifacts, artifact-card, library-page's table column and preview pane) and their tests.
• Verified `ArtifactUploadResponseSchema`/`ArtifactCountsSchema` already match the library's routes.

Test plan

• `bunx tsc -p apps/web --noEmit`
• `bun run lint`, `bun run fmt`
• `cd apps/web && bun run build && bun test ./src` (582 pass)

[linear-code]

CL-8515