feat: add GET /auth/miners endpoint

[paragmore]

Unified miner listing endpoint that replaces direct listThings RPC calls from the frontend.

• Clean field name mapping for filters, sorts, and projections (firmware instead of
  last.snap.config.firmware_ver)
• Field projection filters response to only requested fields — excludes unrequested fields like hashrate,
  power, efficiency
• Overfetch offset + limit from each ork with parallel lightweight count query ({id:1}) for accurate
  totalCount
• Batch fetching when requested page exceeds RPC_PAGE_LIMIT
• App-node side sorting across multi-ork results
• Optional pool hashrate enrichment via getWrkExtData