NPE Claims Should Use Binary Format Instead of JSON

## Issue

Currently, NPE (Non-Person Entity) claims are transmitted as JSON in HTTP requests to authnz-rs. This is inconsistent with the NanoTDF binary format used elsewhere in the architecture.

## Current State

**arkavo-edge → authnz-rs (authentication)**: JSON
```json
{
"platform_code": "macos-arm64",
"platform_state": "Trusted",
"device_id": "...",
"app_version": "0.38.2"
}
```

**authnz-rs → arkavo-edge (response)**: NTDF binary token (Z85 encoded)
```
Authorization: NTDF
```

## Proposal

NPE claims should be serialized as binary (matching NanoTDF format) and Z85 encoded for transport, rather than using JSON.

**Benefits:**
1. Consistency with NanoTDF binary format
2. Smaller payload size
3. Unified serialization approach
4. Better alignment with RATS attestation evidence formats

## Impact

- authnz-rs API changes (breaking)
- arkavo-edge client changes
- Update NTDF token specification
- Migration path for existing deployments

## Related Work

- NTDF token specification: `ntdf-token/draft-arkavo-ntdf-token-00.md`
- NanoTDF implementation: `opentdf-rs`
- arkavo-edge implementation: Issue #309

Read ntdf-token/draft-arkavo-ntdf-token-00.md first, then compare the NanoTDF implementation in opentdf-rs with the arkavo-edge implementation referenced as Issue #309. The work is done when the binary NPE claim format, Z85 transport, authnz-rs and arkavo-edge API changes, NTDF specification updates, and migration path for existing deployments are defined.

Written by the indexing model from the issue text.