Expose report and dataset operations through OCS

[Rello]

Add versioned OCS endpoints in the existing ApiController for report listing, metadata and saved-filter data, owned dataset listing, and adding/updating or deleting dataset rows. Existing non-OCS URLs and payloads remain compatible.

Report reads include user, group and folder shares and reuse the viewer backend pipeline for saved filters, variables, sorting and transformations. Metadata excludes connection settings and share secrets. Public-link-only and panorama-only access are excluded; browser-side formatting and pivots remain client-side.

Dataset operations delegate directly to the existing V3 list and V4 write handlers, preserving ownership checks, validation, version updates and notifications. Writes require owned legacy datasets; flexible datasets retain the stable-column record API. V4 application errors remain success=false inside ocs.data with HTTP 200, as documented in openapi.json and the API guide.

Validation: 229 unit tests / 733 assertions passed. Live local Nextcloud checks covered report listing/metadata/data, authentication and missing-report errors, the unchanged V3 list, OCS dataset listing and both writes rejecting an inaccessible dataset. Successful dataset writes and shared access were not exercised live. OpenAPI JSON and schema references checked; no full OpenAPI validator run.

No duplicate Moment/dependency changes or unrelated Composer constraint edit included.

Assisted-by: Codex:GPT-5