runAllowancePreflightCheck cannot see any protocol write node, so 130 write actions are invisible to it

## Reason

`runAllowancePreflightCheck` reads the method from `cfg.abiFunction` (`lib/mcp/validate-workflow.ts`). A protocol node has no such field: its config is `actionType: "/"` plus a `_protocolMeta` blob. `isWriteActionType` does not match one either, because the `protocol-write` string is the `stepImportPath` at `lib/protocol-registry.ts:505`, not the config value.

So the warning is reachable only from `web3/write-contract` and `web3/batch-write-contract`, and all 130 write actions across the 24 registered protocols are unchecked.

## Plan

Resolve the method per node type: `cfg.abiFunction` for raw web3 nodes, `_protocolMeta.functionName` for protocol nodes, gated on that blob's own `actionType === "write"`.

Do not widen `isWriteActionType`; `lib/mcp/action-type.ts:23-32` says why.

Then widen `ALLOWANCE_SPEND_METHODS` past the current three, including only names whose every use in the catalogue is allowance-consuming and whose standard ERC-20 / ERC-4626 / ERC-721 meaning agrees.

## Scope

Ships and is correct with #2110 and the approve-warning seam absent. Warnings only: `valid` is computed from `errors`, so nothing here can flip a workflow to invalid.

Found by @cgair while implementing #2110, which is being split into three independently shippable seams. Baseline pinned by `tests/unit/validate-workflow-seed-workflows.test.ts`, which passes today because the seed corpus contains no `web3/write-contract` or `web3/batch-write-contract` nodes.

Start in lib/mcp/validate-workflow.ts, then read lib/protocol-registry.ts:505 and lib/mcp/action-type.ts:23-32 to understand node configuration and write-action matching. Run tests/unit/validate-workflow-seed-workflows.test.ts and inspect the protocol catalogue and allowance method list. Done means protocol write nodes receive the intended allowance warnings without changing workflow validity or widening isWriteActionType.

Written by the indexing model from the issue text.