SDK + CLI: getPositions() to fetch all wallet lend positions in one call

[its-everdred]

Closes #454

Summary

Adds getPositions() to the SDK to fetch all of a wallet's lend positions in one call, replacing the per-market getPosition fan-out that every portfolio consumer had to write by hand. Wires it through the CLI and the demo.

SDK

• GetPositionsParams (chainId?, provider?, nonZeroOnly?), exported from the public entry.
• LendProvider.getPositions(walletAddress, params?) — walks the provider's market allowlist and fetches each position with Promise.allSettled, so a single bad-market RPC can't poison the batch (rejected markets are dropped).
• BaseLendNamespace.fetchPositions — aggregates across configured providers (or one, via provider), flattens, then applies nonZeroOnly.
• ActionsLendNamespace.getPositions(walletAddress, params?) and WalletLendNamespace.getPositions(params?) (uses wallet.address implicitly).

CLI

• actions wallet lend positions [--chain <name> | --chain-id <id>] [--non-zero-only] — one wallet.lend.getPositions() call; emits LendMarketPosition[] verbatim (bigints stringified). New lendPositions output sink.

Demo

• Backend: getLendPositions service + GET /wallet/lend/positions route/controller (optional chainId/nonZeroOnly query).
• Frontend: actionsApi.getPositions, EarnOperations.getPositions on both wallet operation builders.
• useLendProvider.ts: both fan-out sites (mount load + post-trade refresh) now call operations.getPositions() once. The single getPosition activity-log entry is now honest (one call, one line).

Testing

• SDK: provider walk / empty allowlist / missing-address / chain validation / per-market failure isolation; namespace aggregation / provider filter / nonZeroOnly; wallet implicit-address path.
• CLI: emit shape, --chain + --non-zero-only forwarding, multi-chain rejection, missing-lend/RPC error mapping.
• Backend: service param-forwarding + bigint serialization + error propagation.
• All suites green (SDK 673, CLI 267, backend 132, frontend 73); typecheck + lint clean across packages.
• Manual CLI run against the demo config (Base Sepolia + OP Sepolia): default aggregates both chains; --non-zero-only → []; --chain base-sepolia filters; both-flags rejected with a validation error.

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