fix: typed data for another chain cannot be signed (closes #519)

EIP-712 has a wallet refuse typed data whose domain chainId is not the
active chain, because the signature is valid on the chain it names. The
sign screen now shows such a request with the reason on its error line
and Sign disabled, the same way it refuses a mismatched primary type.
The background checks again when the signature comes back, against the
network active then, and answers the site with that refusal instead of
the signature. A chain id is read as ethers signs it, so 1, "1" and
"0x1" are one chain. Typed data with no chainId signs as before.

Model: opus-5-5

README.md

@@ -2160,6 +2160,13 @@ view would leave a wallet one click from deletion.
     - Typed data that states no primary type, or one other than the type it
       would be signed as, or that cannot be read → shown with the error line
       saying so and "Sign" disabled; only "Reject" remains
+    - Typed data whose domain `chainId` names a chain other than the active
+      network's → shown with the error line naming both chain ids and "Sign"
+      disabled; only "Reject" remains. EIP-712 asks for this, because the
+      signature is valid on the chain the domain names. Typed data with no
+      `chainId` is not refused. The background refuses such a signature too,
+      against the network active when the signature reaches it, and answers the
+      site with the same sentence
     - A `personal_sign` or `eth_sign` message that is not hex (`0x` or `0X` and
       an even number of hex digits, the form ethers' `getBytes` reads when
       signing) → shown as plain text, with the error line "This message is plain