Add classification review and safeguard explanation to authoring and catalog UX

Tracked by #590. Depends on #592 and #593. Coordinate with editor epic #399 and structured diagnostics #396.

## Outcome

Authors, reviewers, operators, and catalog consumers can inspect field concepts, classifications, provenance, review state, and effective safeguard requirements without reading raw YAML or exposing source values.

## Requirements

- Provide a field-oriented review view showing:
- dataset, entity, and field name;
- physical type;
- primary and additional semantic concepts;
- classification facet and term;
- vocabulary/profile identity and version;
- declared, derived, or proposed provenance;
- review state;
- effective safeguard requirements and enforcement status.
- Support filtering by concept, classification, vocabulary/profile, review state, and enforcement status.
- Keep labels human-readable while retaining immutable IRIs and stable rule IDs underneath.
- Explain why a classification or control applies and which reviewed artifact supplied it.
- Use the exact compiled metadata and explanation contracts rather than reimplementing semantic or policy logic in a UI.
- Integrate authoring diagnostics with #396 and later editor clients under #399.
- Keep unreviewed suggestions visually and structurally distinct from accepted classifications.
- Do not inspect live registry values or trigger scripts, connectors, or network vocabulary lookups as a side effect of browsing metadata.
- Respect existing catalog metadata authorization and avoid widening public schema discovery accidentally.

## Acceptance criteria

- [ ] A reviewer can inspect a table-like field inventory with typed classification badges and authoritative concept sources.
- [ ] Every displayed control links to a value-free explanation and stable rule ID.
- [ ] Unreviewed suggestions cannot be mistaken for released metadata or active policy.
- [ ] Filtering and search operate only over bounded compiled metadata.
- [ ] The UI renders PublicSchema, EU SEMIC, and local vocabulary bindings without privileging one hardcoded namespace.
- [ ] Authorization tests prove restricted metadata does not become public through the new view.
- [ ] A clean authoring journey is documented and tested separately from runtime enforcement.

## Non-goals

- A general data marketplace
- Source-data profiling or sampling
- Policy activation from a browser click without the governed config workflow
- Duplicating Registry compiler or PDP logic in frontend code
- Editor-specific language-server implementation already tracked by #399

Commencez par lire les issues suivies et dépendantes #590, #592, #593, #396 et #399, puis localisez les contrats existants relatifs aux métadonnées compilées et aux explications. Le travail est terminé lorsque la vue de revue orientée champ, le filtrage borné, les explications exemptes de valeurs, la couverture de l’autorisation et le parcours de création documenté séparément satisfont aux critères d’acceptation indiqués.

Rédigé par le modèle d'indexation à partir du texte de l'issue.