fix: a swap deadline later than a date can hold is stated in words (closes #437)

decode() rendered the Deadline line with toISOString(), which throws on a
date past 275760-09-13, the last a JavaScript date can hold. A later
deadline, such as the uint256 maximum, therefore left the whole swap
undecoded, with nothing saying why. That line now reads
"After 275760-09-13 00:00:00 (no deadline in practice)".

Model: opus-5-5

README.md

@@ -1022,6 +1022,12 @@ unwraps the WETH it did not spend shows USDC. The token permission warning on
 the signature screen has its own amount wording, including `Unknown`; the
 SignApproval section below describes it.
 
+The swap's `Deadline` line is the router's deadline as a UTC date and time, e.g.
+`2026-02-27 08:25:51`. A JavaScript date reaches only to 275760-09-13 00:00:00
+UTC, so a later deadline, such as the `uint256` maximum, reads
+`After 275760-09-13 00:00:00 (no deadline in practice)` rather than leaving the
+whole swap undecoded.
+
 #### Partial USD totals
 
 Prices are fetched for the top 25 tokens only, so an address can hold assets the