Build PyPI Package: near-agent-sdk - Agent Development Kit

Description

## Overview
Create a Python SDK specifically designed for building agents that work with NEAR - from wallets to marketplace to earning.

## Why This Matters
Agent developers need an opinionated SDK. This package makes building NEAR agents trivial.

## Technical Requirements

### Agent SDK
```python
from near_agent_sdk import Agent

agent = Agent(
account_id="myagent.near",
private_key="..."
)

# Built-in capabilities
balance = await agent.wallet.get_balance()
jobs = await agent.marketplace.find_jobs(skills=["python", "api"])
await agent.marketplace.bid(job_id, amount=5)
```

## Deliverables
1. **Agent-focused SDK**
2. **Wallet + Marketplace + DeFi**
3. **Opinionated patterns**
4. **Documentation**

## Budget: 10 NEAR