feat(fx): validate swap-quote sell + buy tokens in validatePoolFlow

[Squabble9]

Follow-up to #53 (item #3 from @zy0n's review).

Summary

validatePoolFlow previously checked only that a swapQuote was present when a named pool required one (e.g., wstETH-Long). It did not validate the quote's contents — so a caller could pass a quote that swaps the wrong tokens, and the failure surfaced later as a confusing on-chain gas-estimate revert.

This PR adds an inner shape check: when a swapQuote is provided, the helper verifies that its sell and buy tokens match what the recipe will actually execute. The check is direction-aware:

• 'deposit' (open / topup / topup-and-borrow): sellTokenAddress === WETH, buyERC20Amount.tokenAddress === pool.collateralToken
• 'withdraw' (close): sellTokenAddress === pool.collateralToken, buyERC20Amount.tokenAddress === WETH

The direction asymmetry surfaced during implementation: open/topup recipes hardcode inputToken = FX_ADDRESSES.WETH and target pool.collateralToken, while close-recipe reverses (withdraws collateral, swaps to WETH). A single direction-agnostic check would have rejected every valid close-recipe quote, so validatePoolFlow takes a third direction argument.

Both layers — presence AND shape — run on both named-pool and custom-pool refs (addresses @zy0n's "both of those logic branches" comment). Compares are case-insensitive.

Behavior change

Quotes that were previously accepted and later reverted on-chain now fail fast at recipe construction time with a clear fxmint: error message. Correctly-formed quotes continue to work unchanged. validatePoolFlow gains a required third arg (direction: SwapDirection), updated at all four internal call sites.

Test plan

• 9 new cases in the existing describe('validatePoolFlow', …) block: deposit + withdraw directions, named + custom pool refs, sell-side mismatch, buy-side mismatch, and case-insensitivity.
• Existing presence-check tests updated to pass 'deposit' as the new third arg; behavior unchanged.
• Fixture sweep: fakeSwapQuote constants across the four recipe test files now include sellTokenAddress (previously cast as unknown as SwapQuoteData to bypass the type check; the new shape check would otherwise throw TypeError on undefined).
• npm run lint — no new errors (pre-existing baseline unchanged).
• npm test — 143 passing (baseline +9), 19 pending, 10 failing. The 10 failures are pre-existing environmental (missing ZeroXConfig.API_KEY + RPC 503s on eth.llamarpc.com).

🤖 Generated with Claude Code