feat(annotations): add cursor pagination and individual access by ID

[martsokha]

Context

Annotations support create and list but lack cursor-based pagination and individual access by ID, inconsistent with other resource endpoints.

Requirements

• Add cursor-based pagination to GET /workspaces/{workspaceId}/annotations/
• Add GET /annotations/{annotationId}/ for individual annotation access
• Add PATCH /annotations/{annotationId}/ for updating annotations
• Add DELETE /annotations/{annotationId}/ for removing annotations
• Follow the same workspace-scoped creation / direct-access-by-ID pattern used by other resources

References

• Server docs: ARCHITECTURE.md - API Surface