[Feature]: native wallet setup and cross-chain funding

### Description

Every payment prerequisite currently happens outside ipfs2foc. The README sends users to filecoin-pin (`npx filecoin-pin@latest payments setup --auto`) for the USDFC deposit and FWSS operator approval, and assumes the wallet already holds FIL and USDFC. That is two tools and a funding scavenger hunt before the first `ipfs2foc` command that touches chain.

filecoin-project/filecoin-pin#637 (draft) adds interactive cross-chain funding to `payments fund`: acquire the FIL needed for gas and the USDFC needed for the deposit from Arbitrum, Ethereum, Base, and other chains, with route planning in [squid-evm-funding](https://github.com/FilOzone/squid-evm-funding). Once that lands, ipfs2foc should offer the same capability natively so a migration never requires a second tool.

### Scope

1. Wallet setup inside ipfs2foc: USDFC deposit plus FWSS operator approval, the equivalent of `payments setup --auto`.
2. Funding: when the wallet has a FIL or USDFC shortfall, offer the squid-evm-funding swap path from filecoin-pin#637.
3. Docs: drop the filecoin-pin detour from the README and quickstart once both work natively.

### Dependencies

filecoin-pin#637 needs to land first. It validates the squid-evm-funding route on mainnet, and ipfs2foc should consume the same library at the version that run proves out.

Start with the README and quickstart payment prerequisites, then review filecoin-pin#637 and the squid-evm-funding route validation before choosing the integration entry point. Done means native wallet setup, shortfall funding, and updated documentation replace the filecoin-pin detour without requiring a second tool.

Written by the indexing model from the issue text.