feat: Implement versioning documentation

docs/versioning/API.md

@@ -0,0 +1,34 @@
+# API Reference
+
+**Complete API documentation for versioning functions and hooks**
+
+## Database Functions
+
+### create_relational_version()
+Trigger function - automatically creates versions on entity INSERT/UPDATE.
+
+### get_version_diff(entity_type, from_version_id, to_version_id)
+Returns JSONB diff between two versions.
+
+### cleanup_old_versions(entity_type, keep_versions)
+Deletes old versions, keeping N most recent per entity.
+
+### rollback_to_version(entity_type, entity_id, target_version_id, changed_by, reason)
+Restores entity to previous version, creates new version with change_type='restored'.
+
+## React Hooks
+
+### useEntityVersions(entityType, entityId)
+Returns: `{ versions, currentVersion, loading, rollbackToVersion, ... }`
+
+### useVersionComparison(entityType, fromVersionId, toVersionId)
+Returns: `{ diff, loading, error }`
+
+## Components
+
+- `<VersionIndicator />` - Version badge
+- `<EntityVersionHistory />` - Full timeline
+- `<VersionComparisonDialog />` - Side-by-side diff
+- `<RollbackDialog />` - Restore confirmation
+
+See [FRONTEND.md](./FRONTEND.md) for detailed usage.