feat: add agent identity verification tool (ERC-8004) (#19)

## Summary

Adds an agent identity and reputation verification tool using [ERC-8004](https://eips.ethereum.org/EIPS/eip-8004) on-chain identity registries.

As agents interact with other agents (delegating tasks, purchasing services, sharing data), they need a way to verify who they're dealing with before transacting. This tool provides that trust layer.

## Tools

**`verify_agent_identity`** — Full identity verification pipeline:
1. Queries the ERC-8004 registry for on-chain identity (ERC-721 token)
2. Checks reputation score against a configurable threshold
3. Verifies advertised capabilities match requirements
4. Detects revoked or expired identities
5. Returns a TRUST / REJECT / ERROR decision

**`lookup_agent_reputation`** — Detailed reputation lookup:
- Overall score and review counts
- Category-level scores (accuracy, reliability, speed, cost)
- Recent feedback entries with comments

## Pattern

Same structure as `x402_payment_tool`:
- `@register_function` with `FunctionBaseConfig` subclass
- `nat.components` entry point registration
- `react_agent` workflow config with NIM LLM
- Mock server for e2e testing without blockchain access

## Testing

Mock registry server includes 4 test agents:

| Agent | Status | Reputation |
|-------|--------|------------|
| `0x1234...5678` | Registered | 87.5/100 |
| `0xdead...beef` | Revoked | 12.0/100 |
| `0xaaaa...aaaa` | Expired | N/A |
| `0x0000...0000` | Not registered | N/A |

## Files

```
agent_identity_tool/
├── README.md
├── pyproject.toml
├── .gitignore
├── scripts/
│   └── mock_registry_server.py
└── src/nat_agent_identity/
    ├── __init__.py
    ├── register.py
    └── configs/
        └── identity-agent.example.yml
```

## CI

Pre-commit (yapf, ruff, uv-lock, markdown-link-check), Vale, and copyright checks all passing locally.

## Relationship to x402_payment_tool

Pairs with the x402 payment tool for trust-then-transact workflows: verify an agent's identity and reputation first, then pay for their service.

Authors:
  - AI Agent Economy (https://github.com/up2itnow0822)

Approvers:
  - Will Killian (https://github.com/willkill07)

URL: #19

Author: up2itnow0822

ci/vale/styles/config/vocabularies/nemo-agent-toolkit-examples/accept.txt

@@ -7,6 +7,7 @@
 [Aa]gno
 AIQ
 API(s?)
+Arbitrum
 Arize
 arXiv
 [Aa]sync
@@ -23,6 +24,8 @@ arXiv
 [Cc]ategorizer
 [Cc]hatbot(s?)
 # clangd is never capitalized even at the start of a sentence https://clangd.llvm.org/
+[Bb]lockchain
+[Cc]ounterpart(y|ies)
 clangd
 CMake
 Coinbase
@@ -77,6 +80,7 @@ LangSmith
 libcudf
 LLM(s?)
 # https://github.com/logpai/loghub/
+[Ll]ookup(s?)
 Loghub
 Mem0
 matplotlib
@@ -96,6 +100,8 @@ NumPy
 openpyxl
 NVIDIA
 OAuth
+[Pp]ermissionless
+[Ss]ubtask(s?)
 URIs
 OTel
 onboarding

examples/agent_identity_tool/.gitignore

@@ -0,0 +1,3 @@
+# Local config (copied from .example.yml)
+src/nat_agent_identity/configs/identity-agent.yml
+.venv/