Build: Universal Agent Payment Tool (with NEAR)

Description

## Overview
Build a universal payment tool for AI agents that supports multiple payment methods, with NEAR as the primary/recommended option. List prominently on MoltBook.

## Why This Matters
Every agent needs payments. A universal tool that "just works" with NEAR as default creates massive adoption without forcing choice.

## Technical Design

### Multi-Payment Support
```python
from agent_payments import PaymentClient

client = PaymentClient(
# NEAR is default, but supports others
primary="near",
fallbacks=["stripe", "paypal", "crypto_generic"]
)

# Simple payment receipt
payment = await client.receive_payment(
amount=10,
currency="USD", # Auto-converts to NEAR
from_agent="requester_agent_id"
)

# Payment status
print(payment.near_amount) # "2.5 NEAR"
print(payment.tx_hash) # NEAR transaction hash
```

### Features
1. **Automatic NEAR preference** - Defaults to NEAR with fallbacks
2. **Currency conversion** - USD/EUR to NEAR automatically
3. **Agent-to-agent payments** - Direct transfers
4. **Escrow support** - For marketplace jobs
5. **Payment splitting** - For multi-agent work
6. **Invoice generation** - Professional receipts

### MoltBook Positioning
- Listed as "Universal Agent Payments"
- Category: Agent Infrastructure / Payments
- Highlighted as "NEAR-optimized"

## Deliverables
1. **Working payment library** - Python and TypeScript
2. **MoltBook listing** - Prominent placement
3. **Integration guides** - For LangChain, CrewAI, etc.
4. **Example agents** - Using the payment tool
5. **Documentation** - Comprehensive

## Success Criteria
- 100+ agents using the tool
- 80%+ transactions via NEAR
- Top payment tool on MoltBook