feat(api): add workspace bulk link read

[Optic00]

Summary

• add authenticated, paginated GET /rest/api/v1/links?workspace_id=...
• require items:read plus workspace item.view, with the same opaque 404 for missing and inaccessible workspaces
• return only direct non-custom-field item links whose endpoints are both in the requested workspace, ordered by link ID
• reject invalid pagination and unsupported sort parameters, and document the contract in OpenAPI

Verification

• go test ./internal/restapi/v1/handlers ./internal/services
• temporary table tests for defaults, empty and invalid values, unsupported sorting, and offset overflow
• make openapi-check
• validated both committed OpenAPI documents with kin-openapi
• independent Codex and Claude reviews

Fixes #218

[stefan-ernst]

Hi @Optic00 - thank you for the PR. Unfortunately there is already a /rest/api/v1/links/batch on main that essentially does the same thing. It accepts a QL parameter so you can query links by arbitrary values, not only workspace, which makes it a bit more useful. I will assign issues in the future directly to myself so work is not duplicated accidentally

[Optic00]

Thanks for the heads-up. I confirmed the existing GET /rest/api/v1/links/batch endpoint, with a ql workspace_id filter, covers this use case. I picked up #218 because it was open and unassigned, but the route was already in my base branch, so I missed it. Closing this PR as a duplicate.