feat: add gas tracker with real-time estimates

[AugustoL]

Summary

Add a gas tracker feature showing real-time gas prices and transaction cost estimates.

Features

1. Gas Price Display

Show current gas prices in the navbar or dedicated section:

Gas: 🟢 Low: 15 | 🟡 Avg: 20 | 🔴 High: 25 gwei

2. Gas Price Tiers

• Low (Slow): ~10+ minutes confirmation
• Average (Standard): ~3-5 minutes confirmation
• High (Fast): ~30 seconds confirmation

3. Transaction Cost Estimator

Tool in DevTools to estimate transaction costs:

┌─────────────────────────────────────────┐
│ Gas Estimator                           │
├─────────────────────────────────────────┤
│ Transaction Type: [ETH Transfer ▼]      │
│                                         │
│ Estimated Gas: 21,000                   │
│                                         │
│ Cost Estimates:                         │
│   Low:  0.000315 ETH (~$0.79)          │
│   Avg:  0.000420 ETH (~$1.05)          │
│   High: 0.000525 ETH (~$1.31)          │
└─────────────────────────────────────────┘

4. Common Transaction Types

Pre-configured gas estimates for:

• ETH/native transfer (21,000 gas)
• ERC20 transfer (~65,000 gas)
• ERC20 approve (~46,000 gas)
• NFT transfer (~85,000 gas)
• Uniswap swap (~150,000 gas)
• Custom (user input)

Technical Approach

Data Source

• Primary: RPC eth_gasPrice and eth_feeHistory
• EIP-1559 support: baseFeePerGas + priority fee estimates
• Poll interval: Every 12 seconds (1 block)

Gas Price Calculation

interface GasPrices {
  low: bigint;      // 25th percentile of recent blocks
  average: bigint;  // 50th percentile
  high: bigint;     // 75th percentile
  baseFee: bigint;  // Current base fee (EIP-1559)
}

Network Support

• Ethereum Mainnet (EIP-1559)
• L2s with different gas models:
  • Arbitrum (L1 + L2 gas)
  • Optimism/Base (L1 data fee + L2 execution)
  • Polygon (standard gas)
  • BSC (standard gas)

UI Locations

1. Navbar: Compact gas indicator (optional, toggle in settings)
2. Network page: Gas section with more details
3. DevTools: Full gas estimator tool

Settings

• Show/hide gas in navbar
• Default gas tier preference
• Auto-refresh interval

Acceptance Criteria

• Real-time gas price fetching via RPC
• Low/Average/High tier calculation
• EIP-1559 support (base fee + priority fee)
• Gas estimator tool in DevTools
• Common transaction type presets
• USD cost estimates (requires price integration)
• L2 gas model support
• Navbar gas indicator (optional)

Dependencies

• Price integration - for USD cost estimates

[AugustoL]

fixed on #175