feat(positions): add --defi flag with grouped DeFi view

[graysonhyc]

Summary

• New --defi flag on zerion positions — shorthand for --positions defi plus a DeFi-aware JSON shape (protocols[] → groups[] → tokens[]) grouped by dapp.
• LP positions sharing a group_id collapse into a single pool entry. Loans are netted against deposits in per-protocol totals so the displayed value matches what the user "actually owns."
• Pretty mode renders [position_type] badges colored by polarity: deposit/staked green, loan red, reward yellow, locked cyan.

API mapping

Uses the existing filter[positions]=only_complex route. Enrichment pulls protocol, protocol_module, position_type, group_id, pool_address, and application_metadata from each position's attributes.

Output shape (--defi, JSON)

{
  "wallet": {...},
  "filter": "defi",
  "summary": { "total_value": 4200, "gross_value": 4500, "protocols": 2, "positions": 4 },
  "protocols": [
    { "dapp": "Aave V3", "module": "lending", "net_value": 3700,
      "groups": [
        { "position_type": "deposit", "value": 4000, "tokens": [...] },
        { "position_type": "loan",    "value": 300,  "tokens": [...] }
      ]}
  ]
}

Conflict handling

--defi --positions all|simple → conflicting_flags error. --defi --positions defi is fine (treated as the same intent).

Test plan

• npm test — 173 unit tests pass (6 new for formatDefiPositions)
• node cli/zerion.js positions vitalik.eth --defi --pretty — manual smoke
• node cli/zerion.js positions <addr> --defi --chain ethereum — chain filter still applies
• node cli/zerion.js positions <addr> --defi --positions all — verify conflict error
• Compare against old --positions defi --pretty output to confirm grouping reads better

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