fix: TxApproval links addresses to the explorer of the transaction's network (closes #631)

TxApproval built its From, Contract and decoded-action address links for
the active network, so a Sepolia transaction reviewed with mainnet active
linked to the mainnet explorer. approvalAddressHtml() now takes the
transaction's chain id and passes it to renderAddressHtml(), as SuccessTx
and ErrorTx do. SignApproval and SiteApproval still link for the active
network. The walletDefects fixture's numeric chain id, which names no
network, is now the hex string the background sends.

Model: opus-5-5

README.md

@@ -2395,6 +2395,8 @@ view would leave a wallet one click from deletion.
     - Raw data: full calldata displayed inline (shown if present)
     - Password input and an error line
     - "Confirm" / "Reject" buttons
+- **Behavior**: Every etherscan link on the screen opens the explorer of the
+  network the transaction was populated on, whichever network is active.
 - **Transitions**:
     - "Confirm" (correct password) → decrypts and signs the transaction it was
       shown, exactly as shown, hands the signed transaction to the background to