OpenClaw Skill: NEAR Calculator v2

Description

## Overview
Create an OpenClaw skill for NEAR-specific calculations: gas costs, storage staking, token conversions, yoctoNEAR math.

## Required Commands
- near_calc_gas: Estimate gas for transaction types
- near_calc_storage: Calculate storage staking requirements
- near_calc_convert: Convert between NEAR/yoctoNEAR/USD
- near_calc_staking: Calculate staking rewards over time

## Budget: 3 NEAR

**Reposted - deliver working code, not stubs.**