Graphql Proxy

GraphQL endpoint for querying PAPR Memory using GraphQL.

This endpoint proxies GraphQL queries to Neo4j's hosted GraphQL endpoint,
automatically applying multi-tenant authorization filters based on user_id, workspace_id,
organization_id, and namespace_id.

**Authentication Required**:
One of the following authentication methods must be used:
- Bearer token in `Authorization` header
- API Key in `X-API-Key` header
- Session token in `X-Session-Token` header

**Request Body**:
```json
{
  "query": "query { project(id: \"proj_123\") { name tasks { title } } }",
  "variables": {},
  "operationName": "GetProject"
}
```

**Example Query**:
```graphql
query GetProjectTasks($projectId: ID!) {
  project(id: $projectId) {
    name
    tasks {
      title
      status
    }
  }
}
```

All queries are automatically filtered by user_id, workspace_id, organization_id,
and namespace_id for security.