Preview LLM judge

Run the LLM judge once against a sample response (rule-editor sandbox). `binding_id` runs against a specific candidate instead of the active one.

curl -X POST "https://example.com/dlp/judge/preview" \  -H "Content-Type: application/json" \  -d '{    "instruction": "string",    "sample": "string"  }'

{  "spans": [    "string"  ],  "redacted": "string",  "judged": "string"}