feat: CSV export for SNARK workers

[dannywillems]

Summary

Add the ability to export SNARK worker data as a CSV file, showing who is producing SNARK proofs and earning fees.

Use Case

Users need SNARK worker data for:

• Understanding SNARK work distribution
• Analyzing fee earnings
• Identifying active SNARK workers
• Network health analysis

Requirements

Data to Include

• Public key (SNARK worker address)
• Total fees earned (in MINA)
• Number of SNARK jobs completed
• Average fee per job
• First seen timestamp
• Last seen timestamp

Filtering Options

• Date range picker (from/to)
• Preset ranges: Last 24h, 7 days, 30 days
• Minimum fees threshold (optional)

UI Location

• New "SNARK Workers" section on Analytics page, or
• Dedicated SNARK Workers page (/snark-workers)
• Add "Export CSV" button

CSV Format Example

public_key,total_fees,jobs_completed,avg_fee,first_seen,last_seen
B62qs...,125.5,1250,0.1004,2025-01-01T00:00:00Z,2025-01-15T23:59:00Z
B62qt...,98.2,980,0.1002,2025-01-03T10:00:00Z,2025-01-15T20:30:00Z

Technical Notes

• SNARK worker data comes from feeTransfer in block transactions
• Filter fee transfers by type to identify SNARK fees vs coinbase
• May need to aggregate across many blocks

Acceptance Criteria

• SNARK workers list visible (new section or page)
• Export button available
• Date range filter works correctly
• CSV downloads with descriptive filename
• Sorted by total fees earned (descending)