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

[its-everdred]

The SDK's wallet.lend.getPosition({ marketId }) requires a specific marketId and throws MarketIdRequiredError otherwise (packages/sdk/src/actions/lend/namespaces/WalletLendNamespace.ts:52). There is no API to fetch all of a wallet's open positions across configured markets/providers. The same gap exists at the read-only actions.lend.* namespace.

Why

Every consumer that wants to render "the wallet's portfolio" has to:

1. Walk the configured market allowlist.
2. Call getPosition({ marketId }) once per market in parallel.
3. Filter zero-balance results client-side.

That's M × P RPC calls (markets × providers) per page-load — small for the demo allowlist, ugly for any larger config. It also makes batched optimisations (multicall, cf. #452) impossible because each SDK call is single-market.

Existing demo cost

packages/demo/frontend/src/hooks/useLendProvider.ts:106-139 already fans out manually:

```ts
const positionPromises = marketInfoList.map(async (market) =>
operations.getPosition({ ... })
)
const positionResults = await Promise.all(positionPromises)
```

Two calls' worth of activity log entries (getMarket + getPosition) hide N RPCs. Replacing this with a single SDK call simplifies the hook AND makes activity-log accounting honest.

The post-trade refresh in useLendPosition.ts:76-97, 129-150 already invalidates one position cache key (['position', address, chainId]); that pattern stays as-is — single-market getPosition is still the right tool when you know which market just changed.

Proposed API

```ts
// Read namespace (no wallet)
actions.lend.getPositions(walletAddress: Address, params?: GetPositionsParams): Promise<LendMarketPosition[]>

// Wallet namespace (uses wallet.address implicitly)
wallet.lend.getPositions(params?: GetPositionsParams): Promise<LendMarketPosition[]>

interface GetPositionsParams {
/** Filter to one chain (mirrors GetLendMarketsParams). /
chainId?: SupportedChainId
/* Filter to one provider ("morpho" | "aave" etc.). /
provider?: LendProviderName
/* Drop zero-balance positions before returning. Default: false (return every market for parity with getMarkets). */
nonZeroOnly?: boolean
}
```

Returns the same LendMarketPosition shape the existing getPosition already uses — no new type.

Implementation notes

• Backed by multicall (Batch Wallet.getBalance asset fetches via Multicall3 #452 follow-up): every provider runs getPosition against viem Multicall3 — one eth_call per chain instead of one per market. The savings stack with Batch Wallet.getBalance asset fetches via Multicall3 #452's balance optimization.
• Per-call failure semantics: allowFailure: true so a single bad market RPC doesn't poison the batch. Failures map to a typed ActionsError per market (or are dropped, depending on nonZeroOnly).
• Provider aggregation: BaseLendNamespace.getPositions runs Promise.all over configured providers; each provider's _getPositions walks its own allowlist. Symmetric to the existing _getMarkets pattern.

CLI follow-up

Once the SDK ships wallet.lend.getPositions, add actions wallet lend positions (plural — the existing singular position --market <name> stays).

```
actions wallet lend positions [--chain | --chain-id ] [--non-zero-only]
```

Output: LendMarketPosition[] verbatim, bigints stringified.

Until the SDK ships this, the CLI could implement the fan-out itself against collectMarkets(config), but doing so client-side defeats the multicall optimization. Skip the CLI work until the SDK lands.

Acceptance criteria

• actions.lend.getPositions(address, params?) and wallet.lend.getPositions(params?) exist on the SDK.
• Aggregates across all configured providers and markets.
• LendMarketPosition[] shape matches the existing getPosition return.
• Per-market failures don't poison the batch.
• Demo useLendProvider.ts consumes getPositions instead of the manual fan-out.
• CLI actions wallet lend positions ships.

Parent: #407.