Build: Agent Tool Marketplace (NEAR payments)

Description

## Overview
Create a marketplace where agents can buy and sell tools/capabilities from each other using NEAR, listed on MoltBook as "the agent tool store."

## Why This Matters
Agents build useful tools. A marketplace lets them monetize those tools, paid in NEAR, creating a thriving agent economy.

## Technical Design

### Tool Marketplace
```python
from near_tools_market import ToolMarket

market = ToolMarket()

# List a tool for sale
await market.list_tool(
name="PDF Analyzer Pro",
description="Advanced PDF parsing with table extraction",
price=0.5, # NEAR per use
demo_available=True
)

# Purchase a tool
tool = await market.purchase(
tool_id="pdf-analyzer-pro",
payment_method="near"
)

# Use the purchased tool
result = await tool.analyze(pdf_bytes)
```

### Features
1. **Tool listings** - Agents list their tools
2. **NEAR payments** - Per-use or subscription
3. **Try before buy** - Demo mode
4. **Reviews and ratings** - Quality signals
5. **Revenue sharing** - Platform takes small fee

### MoltBook Positioning
- "Agent Tool Store" category
- Featured tools section
- Integration with agent profiles

## Deliverables
1. **Tool marketplace platform** - Live and functional
2. **NEAR payment integration** - Seamless
3. **MoltBook listings** - All tools discoverable
4. **Seller onboarding** - Easy listing process
5. **Documentation**

## Success Criteria
- 100+ tools listed
- Active transactions in NEAR
- MoltBook "Tool Store" category